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PALEOCEANOGRAPHY, VOL. 22, PA3217, doi:10.1029/2007PA001504, 2007
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A novel approach to dissolution correction of Mg/Ca–based
paleothermometry in the tropical Pacific
Figen Mekik,1 Roger François,2 and Maureen Soon2
Received 28 May 2007; accepted 11 June 2007; published 14 September 2007.
[1] Mg/Ca in planktonic foraminifers carries two main signals: calcification temperature and postdepositional
test dissolution. Shell dissolution thus distorts water temperature reconstructions made with Mg/Ca in
foraminifers. This problem could be resolved by quantifying the impact of carbonate dissolution on Mg/Ca with
an independent, temperature-insensitive deep-sea calcite dissolution proxy, such as the Globorotalia menardii
fragmentation index (MFI). To test the validity of this approach, we measured Mg/Ca in the tests of several
planktonic foraminifers and MFI in core tops collected over a wide geographic region of the tropical Pacific and
covering a wide range of deep-sea calcite dissolution and seawater temperature. We confirm that Mg/Ca from
different species have different susceptibility to temperature and dissolution. Mg/Ca in surface-dwelling
Globigerina bulloides is controlled by calcification temperature and is largely unaffected by carbonate
dissolution estimated from MFI. In contrast, Mg/Ca in deeper dwelling G. menardii is minimally sensitive to
temperature and dominantly affected by dissolution. Mg/Ca in Neogloboquadrina dutertrei and Pulleniatina
obliquiloculata are significantly affected by both temperature and dissolution, and MFI can be effectively used
to correct temperature estimates from these species for calcite dissolution. Additional variables besides
temperature and dissolution appear to control Mg/Ca in Globorotalia tumida, and their identification is a
prerequisite for interpreting elemental shell composition in this species. Combining down-core measurements of
Mg/Ca in multiple foraminifer species with MFI provides a powerful tool for reconstructing past changes in the
upper water column temperature structure in the tropical Pacific.
Citation: Mekik, F., R. François, and M. Soon (2007), A novel approach to dissolution correction of Mg/Ca – based paleothermometry
in the tropical Pacific, Paleoceanography, 22, PA3217, doi:10.1029/2007PA001504.
1. Introduction
[2] Mg/Ca in planktonic foraminifers is widely used as a
proxy for seawater temperature but it carries a double
signal: (1) one for temperature in foraminifer habitat waters
[Nürnberg, 1995; Nürnberg et al., 1996; Rosenthal et al.,
1997; Mashiotta et al., 1999; Lea et al., 1999; Elderfield
and Ganssen, 2000; Lea et al., 2000; Rosenthal and
Lohmann, 2002; Dekens et al., 2002; Lear et al., 2002;
Anand et al., 2003] and (2) one for postdepositional
dissolution of foraminifer shells [Brown and Elderfield,
1996; Rosenthal et al., 2000; Dekens et al., 2002; Rosenthal
and Lohmann, 2002; de Villiers, 2003; Mekik and François,
2006, Regenberg et al., 2006; Fehrenbacher et al., 2006].
This is problematic because the dissolution signal distorts
seawater temperature estimates made with Mg/Ca from
foraminifer shells. In an attempt to resolve this problem,
we explore the possibility of quantifying the contribution of
dissolution to Mg/Ca recorded in foraminifer shells by
combining Mg/Ca measurements with an independent and
1
Department of Geology, Grand Valley State University, Allendale,
Michigan, USA.
2
Department of Earth and Ocean Sciences, University of British
Columbia, Vancouver, British Columbia, Canada.
temperature-insensitive deep sea calcite preservation proxy
that can be easily measured in down core sediment samples.
[3] Our research objectives in this study are (1) to confirm
and further quantify the influence of calcite dissolution on
Mg/Ca in tests of planktonic foraminifers living at different
depths in the water column and (2) to establish whether
temperature estimates made with Mg/Ca can be corrected
for dissolution using the recently developed Globorotalia
menardii fragmentation index (MFI) [Mekik et al., 2002] as
an independent calcite dissolution proxy.
2. Background
2.1. Mg/Ca in Planktonic Foraminifers
[4] The seminal works of several researchers have demonstrated the potential of Mg/Ca in planktonic foraminifers
as a reliable seawater temperature proxy [e.g., Nürnberg,
1995; Nürnberg et al., 1996; Rosenthal et al., 1997;
Hastings et al., 1998; Rosenthal et al., 2000; Elderfield
and Ganssen, 2000; Lea et al., 1999, 2000; Anand et al.,
2003] (the work of Lea et al. [1999] and Anand et al. [2003]
was with sediment traps), but postdepositional calcite dissolution was quickly identified as a possible complicating
factor [e.g., Brown and Elderfield, 1996; Rosenthal et al.,
2000; Rosenthal and Lohmann, 2002; Dekens et al., 2002;
de Villiers 2003; Fehrenbacher et al., 2006; Regenberg et
al., 2006; Mekik and François, 2006].
Copyright 2007 by the American Geophysical Union.
0883-8305/07/2007PA001504$12.00
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[5] Rosenthal et al. [2000] documented a decrease in
foraminifer shell weight with decreasing G. sacculifer
Mg/Ca in core tops from the Ontong Java Plateau
(OJP). Subsequently, Rosenthal and Lohmann [2002]
showed that Mg/Ca in planktonic foraminifers decreased
with increasing water depth and therefore calcite dissolution. They provided dissolution corrected calibrations of
Mg/Ca paleothermometry by using size normalized foraminifer shell weight as a proxy for dissolution [Broecker
and Clark, 1999, 2001a, 2001b, 2003].
[6] Dekens et al. [2002] illustrated the dissolution effects
on Mg/Ca from Globigerinoides ruber, Globigerinoides
sacculifer and Neogloboquadrina dutertrei and derived
multiple equations which correct Mg/Ca – based temperature
estimates for DCO=3 (which is [CO=3 ] of in situ waters minus
the [CO=3 ] at saturation) in core top samples with wide
geographic distribution. Furthermore, Dekens et al. [2002]
described the two surface dwellers, G. ruber and
G. sacculifer, as having a smaller dissolution signal than
the thermocline dweller, N. dutertrei. While Fehrenbacher
et al.’s [2006] work seems to confirm this, Regenberg et al.
[2006] found significant decrease in Mg/Ca in G. ruber and
G. sacculifer with increasing carbonate ion undersaturation
in core tops from the Caribbean.
[7] de Villiers [2003] used Mg/Ca in G. ruber and
G. sacculifer to illustrate the effect of dissolution in down
core work on the OJP by comparing the trends in Mg/Ca
with Le and Shackleton’s [1992] fragmentation index data
and G. sacculifer shell weight. However, neither dissolution
proxy used in this study (fragmentation percent and shell
weight) quantifies percent calcite dissolved. Instead they
show relative dissolution variability in down core work.
[8] Instead of using an independent estimator of calcite
dissolution, Fehrenbacher et al. [2006] used cores taken
along a depth transect on the Ceara Rise and applied Dekens
et al.’s [2002] equations down core. Assuming that DCO=3
is the sole driver of dissolution in their samples and that the
shallowest core experienced minimal or no dissolution, they
reconstructed deep sea carbonate chemistry between the
modern and the Last Glacial Maximum.
[9] Our present contribution to this growing body of
knowledge on both temperature and dissolution effects on
foraminifer Mg/Ca is in testing whether MFI can be used to
independently quantify the decrease in Mg/Ca induced by
calcite dissolution when making temperature estimates. MFI
quantifies the percent of calcite dissolved in individual
samples, not just the relative change in preservation, and
takes into account dissolution resulting from undersaturation in the water column and metabolic CO2 generation in
sediment. The method is also not restricted to depth transects
and can be applied to individual cores.
2.2. Tracing Deep Sea Calcite Dissolution
[10] Most deep sea calcite dissolution proxies, whether
solely based on foraminifer shell weight/fragmentation or
chemistry, are calibrated against CO=3 saturation of bottom
waters [e.g., Broecker and Clark, 1999, 2001a, 2001b, 2003;
Dekens et al., 2002; Marchitto et al., 2005; Regenberg et al.,
2006; Fehrenbacher et al., 2006]. However, the organic
carbon flux reaching the seabed is also an important
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contributor to calcite dissolution in sediments, which results
from the regeneration of metabolic CO2 in pore waters
[Emerson and Bender, 1981]. More precisely it is the ratio
of organic carbon to calcite fluxes reaching the seabed (rain
ratio) that drives dissolution in addition to DCO=3 [Archer
and Maier-Reimer, 1994; Mekik et al., 2002, 2007]. It is
thus imperative to take organic carbon fluxes into account
when quantifying calcite dissolution, particularly in regions
with large spatial variations in carbon flux.
[11] We choose the G. menardii fragmentation index
(MFI) [Mekik et al., 2002] as our independent calcite
dissolution proxy because it has been calibrated against
model-derived estimates of percent calcite dissolved. The
model (Muds) [Archer et al., 2002] takes into account both
bottom water DCO=3 and respiratory calcite dissolution in
the sediments [Mekik et al., 2002, 2007] when calculating
percent calcite dissolved for each coring location. Subsequent to MFI’s calibration, Mekik and François [2006]
demonstrated clear, linear relationships between Mg/Ca in
P. obliquiloculata and G. menardii shells and both bottom
water DCO=3 and MFI-based percent calcite dissolved
estimates for core top samples on the OJP (where variations
in sea surface temperatures are minimal), and thereby
independently corroborated the validity of MFI as a dissolution proxy. Later, F. Mekik and L. Raterink (Effects of
surface ocean conditions on the quantification of deep sea
calcite dissolution using shell weight and fragmentation on
planktonic foraminifers, submitted to Paleoceanography,
2007, hereinafter referred to as Mekik and Raterink, submitted manuscript, 2007) found no clear correlation
between MFI and water temperature at 75 m depth for
samples subjected to similar dissolution (Figure 1) indicating that MFI clearly meets our criteria of temperature
insensitivity.
3. Methods
3.1. Sampling Method
[12] We used 56 core top samples from the eastern
equatorial Pacific (EEP) and OJP (Figure 2) to generate
MFI and Mg/Ca data from five species of planktonic
foraminifers: Globigerina bulloides, Pulleniatina obliquiloculata, Globorotalia tumida, G. menardii and N. dutertrei.
These regions provide samples subjected to a wide range of
sea surface temperature and deep sea calcite dissolution
which is useful for isolating their respective effects on Mg/
Ca of foraminifer shells. The OJP, in particular, provides a
test area where temperature is almost invariable, but where
there is a strong gradient of dissolution with water depth.
All Mg/Ca data from the EEP and Mg/Ca from G. bulloides
are new. Mg/Ca data from OJP for the other four species
were published by Mekik and François [2006].
[13] All samples are from gravity cores to minimize core
top disturbance. About half of our samples overlap with
those used by Loubere [2001] who measured d18O and d13C
from N. dutertrei shells. The regional d 18O and d13C map
produced by Loubere [2001] confirms that our core tops are
modern. Mekik et al. [2007] generated additional d 18O data
for five of our deepest cores and excluded two of these five
samples because their d 18O were more consistent with LGM
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values. Further corroboration that our samples are modern
come from the rain ratio maps [Mekik et al., 2002, 2007]
generated from most of the same samples used herein, which
show regional surface ocean productivity patterns consistent
with satellite-based productivity estimates [Behrenfeld and
Falkowski, 1997] for the EEP.
[14] One of the species we analyzed, G. bulloides, is a
surface dweller (0 – 60 m habitat depth [Schiebel et al.,
1997]), and the other four are thermocline dwellers:
P. obliquiloculata (50 – 100 m [Anand et al., 2003] and 50
m [Farmer et al., 2007]), G. menardii (50 – 100 m [Bé,
1960] and 75 m [Farmer et al., 2007]), N. dutertrei (50 –
100 m [Anand et al., 2003] but most common in the deep
chlorophyll maximum [Fairbanks et al., 1982; Fairbanks
and Wiebe, 1980; Loubere, 2001]) and G. tumida (50 – 100 m,
[Schweitzer and Lohmann, 1991] and 135 – 175 m [Farmer et
al., 2007]). All five foraminifers typically prefer tropical and
subtropical regions (H. Hilbrecht, Extant planktic foraminifera and the physical environment in the Atlantic and
Indian Oceans, Mitteilungen aus dem Geologischen Institut
der Eidgenossische Technische Hochschule and Universität
Zürich, Neue Folge 300, 93 pp., Zurich, Switzerland, 1996,
available at http://www.ngdc.noaa.gov/mgg/geology/
hh1996/, hereinafter referred to as Hilbrecht, report, 1996),
except G. bulloides which is common in northern and
southern high latitudes as well as upwelling zones in the
tropics [Brock et al., 1992; Duplessy et al., 1981; Hemleben
et al., 1985; Kipp, 1976; Thiede, 1983; van Leeuwen, 1989;
Zhang, 1985; Hilbrecht, report, 1996]. High- and lowlatitude populations of this species may be distinct [Schmidt
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Figure 2. Core top sample distribution. Diamonds show
sampling locations for Mg/Ca data. Dashed lines represent
temperature contours at 75 m water depth after Locarnini et
al. [2006].
and Mulitza, 2002; Kucera and Darling, 2002; Darling et
al., 2003], and cryptic species may be present within each
population [Darling et al., 2003].
[15] All temperature estimates for surface waters are from
Locarnini et al. [2006]. Our full temperature, Mg/Ca and
MFI data set, including the number of foraminifers used per
measurement, are available as online auxiliary material1. We
selected the habitat depths for each species by looking for
the best relationship between Mg/Ca and temperature estimates at 30, 50, 75, 100 and 125 m. For G. bulloides, the
best relationship is obtained with temperature at 30 m which
fits well with the habitat depth reported by Schiebel et al.
[1997]; for P. obliquiloculata, the best fit is at 50 m which is
corroborated by Farmer et al.’s [2007] work; for
G. menardii, we obtain a depth of 75 m which matches
Farmer et al.’s [2007] estimate; and for G. tumida the best
fit is at 125 m water depth, which is also the medial value
between the habitat depth estimates for this species by
Schweitzer and Lohmann [1991] and Farmer et al.
[2007]. On the other hand, we are unable to find a good
statistical relationship between Mg/Ca in N. dutertrei shells
and temperature at any uniform depth. N. dutertrei are
known to prefer the deep chlorophyll maximum [Fairbanks
et al., 1982; Fairbanks and Wiebe, 1980], and habitat
depths for this species were estimated using Loubere’s
[2001] isotopic equilibrium depths based on a combination
of d 18O and d13C from N. dutertrei shells. For samples
beyond Loubere’s [2001] data set (those from the OJP and
some samples from the EEP) the average temperature
between 50 and 75 m is used because this is the general
habitat depth range for N. dutertrei in Loubere’s [2001]
work.
3.2. Sample Preparation
[16] Foraminifers were picked within small size ranges
(100 mm or smaller) but from larger foraminifer size
groups than is commonly used in Mg/Ca work [e.g., Anand
Figure 1. MFI versus water temperature at 75 m for all
samples from the EEP. All temperature data are from
Locarnini et al. [2006].
1
Auxiliary materials are available at ftp://ftp.agu.org/apend/pa/
2007pa001504.
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Figure 3. Reproducibility between duplicate Mg/Ca
measurements. Bars show analytical error margins.
et al., 2003; Dekens et al., 2002; Lea et al., 2000]:
G. bulloides (600– 700 mm), P. obliquiloculata (420– 510
mm), G. menardii (700 – 800 mm), N. dutertrei (400– 500 mm)
and G. tumida (900 – 1000 mm). We used larger foraminifers
within these specific size ranges to maintain consistency
with our former work [Mekik and François, 2006]. Using
larger foraminifers minimizes ontogenetic effects on shells
[Kroon and Darling, 1995] and produces more consistent
results. Elderfield et al. [2002] found, and to an extent
Anand and Elderfield [2005] also, that smaller individuals
calcify faster, and that the Mg/Ca signal in larger individuals
tend to more closely reflect seawater temperatures in which
the foraminifers have calcified. Larger foraminifers have
been shown to also produce more reliable results in d 13C
work [Oppo and Fairbanks, 1989; Elderfield et al., 2002] as
well as in size normalized shell weight measurements
(Mekik and Raterink, submitted manuscript, 2007; J. Bijma,
personal communication, 2006).
[17] All foraminifer picking was done by the same person
(F. Mekik) to minimize bias; and instead of trapping
foraminifers between two sieves, they were individually
picked within designated size ranges to improve size
consistency. We used the cleaning protocol of Barker et
al. [2003] as modified by Mekik and François [2006]. We
did not employ rigorous cleaning techniques involving a
reductive step because Rosenthal et al. [2004] have shown
that such methods cause shell dissolution and bias results.
3.3. Analytical Method
[18] The Element 2 Inductively Coupled Plasma Mass
Spectrometer (ICP-MS) at the University of British Columbia (Vancouver, British Columbia) and the methods reported
by Rosenthal et al. [1999] were used for the determination
of Mg/Ca from our foraminifer samples. We prepared
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standard solutions gravimetrically and all standard and
sample solutions were made with 0.075 M nitric acid. We
measured 43Ca to determine [Ca] in all standards and
samples. Matrix effects on Mg/Ca and polyatomic interferences on Ca are insignificant in the concentration ranges we
used in our analyses [Rosenthal et al., 1999].
[19] We made duplicate measurements by dissolving two
separately picked and cleaned foraminifer populations from
each species, in each sediment sample where we had
sufficient number of foraminifers within our designated size
ranges. Figure 3 illustrates the reproducibility between all
our duplicates in relation to the analytical error associated
with each measurement. In Table 1, f represents the
difference between two replicate Mg/Ca measurements for
the same species in the same sediment sample. Mean f for
all measurements is 0.12 mmol/mol, and the standard
deviation in f for all measurements is 0.1 mmol/mol. The
variation coefficient of Mg/Ca in Table 1 is the ratio of the
standard deviation for f in each species to the mean Mg/Ca
from all measurements on that species, represented as a
percentage. Analytical error margins for all data points
(shown as bars on all graphs) are calculated on counting
statistics (66% confidence interval) for the ratio of Mg and
Ca to our internal standard (indium) and the uncertainties on
the intercept and slope of the linear regressions obtained
with our standard solutions.
4. Results
4.1. Globigerina bulloides
[20] Figure 4a shows a strong relationship between Mg/
Ca in G. bulloides and sea surface temperature at 30 m
water depth in samples from the EEP and OJP. We observe a
spread of Mg/Ca values (Mg/Ca ‘‘tail’’) at 29°C. These
samples are from the OJP and represent a wide range of
calcite dissolution. The data in Figure 4a are color-coded to
reflect the extent of dissolution to which each sample was
subjected. MFI’s error margin is 10– 15% dissolved [Mekik
et al., 2002]. We used that margin as the width of our
dissolution brackets.
[21] A clear dissolution signal would be documented by a
gradual color transition from red to green, which is not
observed. This indicates that while Mg/Ca in G. bulloides is
sensitive to temperature, it is not systematically affected by
postdepositional dissolution. This is confirmed by the lack
of correlation between Mg/Ca and MFI-based percent dissolved estimates (Figure 4b). Color coding clearly documents
the overwhelming influence of temperature. Dekens et al.
[2002] found a similar sensitivity to temperature and hardly
any sensitivity to dissolution in their work with Mg/Ca from
Table 1. Mean 8 and Variation Coefficients for Mg/Ca in Five
Species
Foraminifer
Mean 8, mmol/mol
Variation Coefficient, %
G. bulloides
P. obliquiloculata
G. menardii
N. dutertrei
G. tumida
0.13
0.09
0.13
0.16
0.1
2.9
4
6.6
8.8
6.5
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Figure 4. (a) Mg/Ca in G. bulloides versus temperature at 30 m with color-coded dissolution brackets.
(b) Mg/Ca in G. bulloides versus MFI-based percent calcite dissolved with color-coded temperature
brackets.
G. ruber and G. sacculifer, both of which are also surface
dwellers. In contrast, Regenberg et al. [2006] found a
significant dissolution influence on Mg/Ca in G. ruber and
G. sacculifer.
4.2. Pulleniatina obliquiloculata
[22] Figure 5 illustrates plots of Mg/Ca from P. obliquiloculata shells versus temperature at 50 m water depth and
Mg/Ca versus MFI-based percent calcite dissolved in samples from the EEP and OJP. We use the same color coding
to identify the impact of calcite dissolution on the temperature signal (Figure 5a), and a similar color code to reflect
the impact of temperature on the dissolution signal in Mg/
Ca (Figure 5b). On the temperature graph (Figure 5a) we
can identify several dissolution tails (at 24°, 25° and 29°C)
which display a clear color transition. For a given temperature, the samples subjected to higher dissolution clearly
have lower Mg/Ca (green). Likewise when we plot Mg/Ca
versus MFI-based percent calcite dissolved (Figure 5b), we
can see clear grouping of colors and numerous temperature
tails with easily observable color transitions. These results
indicate that Mg/Ca in P. obliquiloculata is systematically
affected by both calcification temperature and postdepositional calcite dissolution.
4.3. Globorotalia tumida
[23] Figure 6 shows the relationship between Mg/Ca from
G. tumida shells and temperature at 125 m and MFI-based
Figure 5. (a) Mg/Ca in P. obliquiloculata versus temperature at 50 m with color-coded dissolution
brackets. (b) Mg/Ca in P. obliquiloculata versus MFI-based percent calcite dissolved with color-coded
temperature brackets.
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Figure 6. (a) Mg/Ca in G. tumida versus temperature at 125 m with color-coded dissolution brackets.
(b) Mg/Ca in G. tumida versus MFI-based percent calcite dissolved with color-coded temperature
brackets.
percent calcite dissolved. The correlation with temperature
is weak, and a wide spread of Mg/Ca values are found at
26°C. Color coding (Figure 6a) indicates that this tail bears
a weak relationship with dissolution. Correlation between
Mg/Ca and MFI for this species (Figure 6b) is also weak.
Factors besides temperature and dissolution that are yet to
be identified thus appear to also affect the Mg/Ca of this
species significantly.
4.4. Neogloboquadrina dutertrei
[24] Plotting Mg/Ca in N. dutertrei shells versus temperature (Figure 7a) at N. dutertrei habitat depths (data for
habitat depths from Loubere [2001]) shows a strong correlation with temperature and possible but ambiguous dissolution tails. This suggests that temperature may have a
significant effect on the Mg/Ca for this species. However,
we also obtain a significant correlation when plotting Mg/Ca
against MFI-based percent calcite dissolved (Figure 7b) and
several temperature tails are clearly visible at 45%, 62%
and 76% dissolved.
4.5. Globorotalia menardii
[25] Plotting Mg/Ca in G. menardii shells against temperature at 75 m (Figure 8a) results in a poor correlation and
clear dissolution tails are identified by progressive color
transitions at 23°, 24° and 29°C. On the other hand, we find
a good linear relationship between Mg/Ca in this species
and MFI-based percent calcite dissolved (Figure 8b) with
little evidence for significant temperature tails, indicating
Figure 7. (a) Mg/Ca in N. dutertrei versus temperature with color-coded dissolution brackets. (b) Mg/
Ca in N. dutertrei versus MFI-based percent calcite dissolved with color-coded temperature brackets.
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Figure 8. (a) Mg/Ca in G. menardii versus temperature at 75 m with color-coded dissolution brackets.
(b) Mg/Ca in G. menardii versus MFI-based percent calcite dissolved with color-coded temperature
brackets.
that Mg/Ca for this species is mainly controlled by calcite
dissolution.
5. Discussion
5.1. Is Dissolution Significantly Affecting Mg/Ca?
[26] Our results show that the strength of the dissolution
signal in Mg/Ca from foraminifer shells is species-specific
(as demonstrated by other studies such as Dekens et al.
[2002], Fehrenbacher et al. [2006], and Regenberg et al.
[2006]). G. bulloides Mg/Ca shows no relationship with
MFI-based percent dissolved estimates in samples from the
EEP and the OJP (Figure 4b). According to Dekens et al.
[2002], it is not uncommon for surface dwellers (G. ruber
and G. sacculifer in their work) to be more sensitive to
temperature and much less so to dissolution or DCO=3 . This
is good news for SST reconstructions because the Mg/Ca of
surface dwellers may not require correction for calcite
dissolution. However, Regenberg et al.’s [2006] results
contradict this finding and the generality of this conclusion
requires further assessment. We observe variations in Mg/
Ca in G. bulloides in OJP samples (2.72– 3.5 mmol/mol,
Figure 4a) that are 1 order of magnitude larger than the
mean reproducibility between G. bulloides sample duplicates (2.2%) where surface ocean temperatures at 30 m are
mostly invariable (29.1°– 29.3°C). Elucidating the cause of
this variation requires further study. Although McConnell
and Thunell [2005] have shown in sediment trap work that
Mg/Ca in G. bulloides records seawater temperatures as
high as 33°C, it is plausible that the OJP is at the upper limit
of temperature sensitivity of Mg/Ca in G. bulloides shells
since this species is more typical of high-latitude regions
Figure 9. Correlation between measured and predicted Mg/Ca (mmol/mol) in P. obliquiloculata using
(a) only temperature as the independent variable and (b) both temperature and MFI-based percent calcite
dissolved as independent variables.
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and upwelling zones in tropical seas [Brock et al., 1992;
Duplessy et al., 1981; Hemleben et al., 1985; Kipp, 1976;
Thiede, 1983; van Leeuwen, 1989; Zhang, 1985; Hilbrecht,
report, 1996]. Another possibility is that there are cryptic
species of G. bulloides on the OJP. Kucera and Darling
[2002] describe 6 genetically distinct groups in the
G. bulloides morphotype. Also, Darling et al.’s [2003]
study clearly demonstrates multiple cryptic species among
G. bulloides in the Santa Barbara Channel. Thus undetected
cryptic species or genotypes may also be at play in the OJP,
however accurately resolving this issue requires the generation of genetic data which is beyond the scope of our work.
[27] In contrast to G. bulloides, we see a clear influence of
dissolution on the Mg/Ca of the four deeper dwelling
foraminifer species. We observe clear tails in the temperature versus Mg/Ca graphs for P. obliquiloculata which can
clearly be related to dissolution (Figure 5). Similar but less
defined tails are also present in the graphs for N. dutertrei
(Figure 7). Plotting MFI-based percent dissolved against
Mg/Ca from G. menardii (Figure 8b) shows a strong linear
relationship between MFI-based percent calcite dissolved
estimates. This suggests that Mg/Ca in this species, like
MFI, may serve as an independent and mostly temperatureinsensitive calcite dissolution proxy but more data from
geographically diverse regions is needed to corroborate this
finding. Mg/Ca for G. tumida, which has keeled shells and
belongs to the same genus, Globorotalia, as G. menardii,
appears to be affected both by temperature and dissolution;
but poorer correlations (Figure 6) suggest that at least one
other factor is also having an important impact. This factor
could be one of many variables such as: (1) Variations in
surface ocean salinity. However, early studies have shown
that salinity is a minor factor controlling Mg/Ca ratios in
foraminifers until salinity variations of 10% or more are
reached [Nürnberg et al., 1996; Lea et al., 1999]. Salinity
variability across our entire study region in the EEP is about
1% [Antonov et al., 2006] so this is an unlikely effect on
our results. (2) Cryptic species within our G. tumida
population. There is evidence of cryptic speciation among
Globorotaliids [Norris et al., 1996], though this has not
been specifically related to G. tumida. While this may likely
be affecting our results, it is very difficult to ascertain
without genetic data. (3) Globorotaliids tend to calcify in
multiple water depths during their lifetime [Elderfield et al.,
2002] and therefore their shell chemistry may be recording
multiple temperatures.
Figure 10. Mg/Ca in N. dutertrei versus temperature in
three dissolution brackets defined by MFI.
5.2. Can Mg/Ca –Based Temperature Estimates be
Corrected for Dissolution?
[28] While Mg/Ca of surface dweller G. bulloides does
not require a dissolution correction to evaluate surface
temperature, our data clearly indicate that this is not the
case for deeper dwelling P. obliquiloculata and N. dutertrei.
Quantifying the effect of calcite dissolution is a prerequisite
before using the Mg/Ca ratio of these species to estimate
their temperature of calcification and potentially reconstruct
past changes in thermocline temperature. We attempt to
address this problem in two ways: (1) by multiple regression
analysis and (2) by grouping our samples into dissolution
brackets (10 –15% dissolved) and deriving individual Mg/
8 of 12
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MEKIK ET AL.: Mg/Ca DISSOLUTION CORRECTION
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Figure 11. Correlation between measured and predicted Mg/Ca (mmol/mol) in G. menardii using (a)
only temperature as the independent variable and (b) both temperature and MFI-based percent calcite
dissolved as independent variables.
Ca – based temperature equations within each dissolution
bracket.
[29] We performed multiple linear regression analysis
using water temperature and MFI-based percent calcite
dissolved as two independent variables against Mg/Ca as
the dependent variable.
[30] For G. bulloides, the linear regression coefficient for
percent dissolved is zero, confirming that calcite dissolution
has insignificant impact on the Mg/Ca of this species.
[31] For P. obliquiloculata, the correlation between measured and predicted Mg/Ca improves markedly when taking
into account both temperature and percent dissolved (R2 =
0.93 versus R2 = 0.80 for temperature alone, Figure 9). The
equation derived from the multiple linear regression (T =
(Mg/Ca + (.015%diss) + 1.7)/0.17; where percent diss is the
MFI-based estimate of calcite percent dissolution) provides
a means of calculating temperature at 50 m depth from Mg/
Ca in P. obliquiloculata and MFI.
[32] On the other hand, for N. dutertrei, the linear
regression does not improve when taking into account
dissolution in addition to temperature (R2 = 0.83 versus
R2 = 0.86 for temperature alone). However, we note a
systematic decrease in the temperature sensitivity of
N. dutertrei Mg/Ca with increasing calcite dissolution
(Figure 10), which may explain the failure of the multiple
linear regression. Reconstruction of temperature at the
chlorophyll maximum using Mg/Ca in this species may
thus be better achieved by using different temperature
equations for different levels of calcite dissolution, but more
data are needed to consolidate the preliminary calibrations
reported in Figure 10.
[33] The regression for Mg/Ca in G. tumida is slightly
improved when taking into account both temperature and
dissolution but remains comparatively weak (R2 = 0.72
versus R2 = 0.68 for temperature alone). Dissolution has a
noticeable effect (e.g., a 50% change in dissolution generates a change in Mg/Ca equivalent to 5°C), but the lower
regression coefficients suggest that factor(s) yet to be
identified affect the Mg/Ca of this species significantly.
[34] In contrast to the other species studied here, Mg/Ca
in G. menardii depends almost only on calcite dissolution.
The linear regression marginally improves when taking into
account temperature in addition to dissolution (R2 = 0.83
versus R2 = 0.80 for dissolution alone, Figure 11). Temperature has thus a noticeable effect on the Mg/Ca of this species
but it is very small (a 10°C change in temperature produces a
change in Mg/Ca equivalent to 7% changes in calcite
dissolution). The equation percent diss = (2.9 – Mg/Ca +
(0.02 T)) /0.028 could be used to take into account this small
effect, if temperature can be independently estimated.
Figure 12. Schematic summary diagram showing relative sensitivity index (I) values for each species.
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MEKIK ET AL.: Mg/Ca DISSOLUTION CORRECTION
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Table 2. Species-Specific Relative Sensitivity Index (I)
Species
D (Mg/Ca)T
D (Mg/Ca)D
I
G. bulloides
P. obliquiloculata
G. tumida
N. dutertrei
G. menardii
2.1
1.7
0.69
0.77
0.2
0
0.75
0.35
0.65
1.4
1.00
0.69
0.66
0.54
0.13
5.3. Comparison of Interspecific Sensitivity to
Temperature and Dissolution in Mg/Ca from
Foraminifer Tests
[35] Figure 12 is a schematic summary diagram illustrating the relative sensitivity of the species examined herein to
temperature as one end-member and dissolution as the other.
Relative sensitivities were quantified by calculating the
change in Mg/Ca resulting from a 10°C change in temperature (D(Mg/Ca)T) and from a 50% change in calcite
dissolution (D(Mg/Ca)D) using the equations obtained from
multiple linear regression (Table 2). A relative sensitivity
index (I) was calculated as
h
i
I ¼ DðMg=CaÞT = DðMg=CaÞT þDðMg=CaÞD
[36] G. bulloides Mg/Ca does not carry a significant
dissolution signal and has a relative sensitivity index of 1.
A species whose Mg/Ca would be affected by dissolution
and totally independent of temperature would have a
relative sensitivity index of zero. Data compiled in Table 2
indicate that the importance of calcite dissolution increases
from P. obliquiloculata (I = 0.69), to G. tumida (I = 0.66),
N. dutertrei (I = 0.54), and G. menardii (I = 0.12)
(Figure 12).
6. Conclusions
[37] Mg/Ca in tests of G. bulloides, P. obliquiloculata,
G. menardii, N. dutertrei and G. tumida has species-specific
responses to calcification temperature and postdepositional
dissolution. We can use MFI as a temperature-insensitive
independent calcite dissolution proxy to quantify the dissolution signal in Mg/Ca and correct temperature estimates
made with Mg/Ca ratios for dissolution.
[38] Mg/Ca from G. bulloides, a surface dweller, has
strong sensitivity to temperature and no quantifiable
relationship with MFI-based percent dissolved estimates
(Figure 4). Mg/Ca in this species, as for other surface
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dwellers, appears to provide a pure temperature signal
although some variability beyond analytical error remains
unexplained.
[39] The other four foraminifers analyzed are all thermocline dwellers. P. obliquiloculata has the strongest sensitivity to temperature but also carries a significant dissolution
signal (Figure 5). Multiple linear regression taking into
account temperature and calcite dissolution provides an
equation which explains nearly all the variability in Mg/Ca
in our samples (R2 = 0.93, Figure 9b) and which can be used
to reconstruct past changes in upper thermocline temperature. Mg/Ca in N. dutertrei shells also carries both a
temperature and a dissolution signal, but is significantly
less sensitive to temperature (Figure 7) than Mg/Ca in
P. obliquiloculata. There is also a clear decreasing trend
in temperature sensitivity with dissolution (Figure 10). We
derived preliminary calibration curves to reconstruct temperature with Mg/Ca in N. dutertrei within three calcite
dissolution brackets which could be used to estimate past
changes in seawater temperature at the deep chlorophyll
maximum. The validity of these equations still needs to be
further tested. Mg/Ca from G. tumida is also sensitive to
temperature and dissolution (Figure 8) but these two variables alone cannot explain all the variability observed (R2 =
0.72). The usefulness of this species hinges on the identification and quantification of the additional factor(s) affecting its Mg/Ca. Finally, Mg/Ca from G. menardii is most
sensitive to calcite dissolution but carries a small temperature signal (Figure 12). Mg/Ca from G. menardii is not
useful for reconstructing thermocline temperature but could
help in reconstructing calcite dissolution, like MFI, if
thermocline temperatures can be independently estimated.
[40] Combining temperature reconstructions using Mg/Ca
from these different species and MFI will provide important
information on the evolution of upper water column thermal
structure of low-latitude oceans.
[41] Acknowledgments. We are very grateful to Paul Loubere for
thought-provoking discussions. Many thanks go to Eelco Rohling and two
anonymous reviewers for their helpful comments which improved our
manuscript. We also extend many thanks to Bert Mueller and the staff from
the Pacific Center for Isotopic and Geochemical Research (PCIGR) at the
University of British Columbia for their help with the ICP-MS. This work
was funded in full by NSF grant OCE0326686. We gratefully acknowledge
the curators and repositories that provided sediment samples and help in
selecting cores for this work (June Padman, Oregon State University; Larry
Peterson, RSMAS; Rusty Lotti-Bond, Lamont-Doherty Earth Observatory;
Warren Smith, Scripps Institution of Oceanography; and curators at the
University of Hawaii). Thanks also go to the National Science Foundation for
the support it provides to those repositories. PCIGR is supported with
funding from NSERC. R.F. is supported by funding from the Canadian
Foundation for Climate and Atmospheric Sciences (CFCAS) and NSERC.
References
Anand, P., and H. Elderfield (2005), Variability
of Mg/Ca and Sr/Ca between and within the
planktonic foraminifers Globigerina bulloides
and Globorotalia truncatulinoides, Geochem.
Geophys. Geosyst., 6, Q11D15, doi:10.1029/
2004GC000811.
Anand, P., H. Elderfield, and M. H. Conte
(2003), Calibration of Mg/Ca thermometry in
planktonic foraminifera from a sediment trap
time series, Paleoceanography, 18(2), 1050,
doi:10.1029/2002PA000846.
Antonov, J. I., R. A. Locarnini, T. P. Boyer, A. V.
Mishonov, and H. E. Garcia (2006), World
Ocean Atlas 2005, vol. 2, Salinity [CD-ROM],
edited by S. Levitus, NOAA Atlas NESDIS,
vol. 62, 182 pp., NOAA, Silver Spring, Md.
10 of 12
Archer, D. E. (1996), An atlas of the distribution of calcium calcite in sediments of the
deep sea, Global Biogeochem. Cycles, 10,
159 – 174.
Archer, D., and E. Maier-Reimer (1994), Effect
of deep sea sedimentary calcite preservation on
atmospheric CO2 concentration, Nature, 367,
260 – 264.
PA3217
MEKIK ET AL.: Mg/Ca DISSOLUTION CORRECTION
Archer, D. E., J. L. Morford, and S. Emerson
(2002), A model of suboxic sedimentary diagenesis suitable for automatic tuning and gridded
global domains, Global Biogeochem. Cycles,
16(1), 1017, doi:10.1029/2000GB001288.
Barker, S., M. Greaves, and H. Elderfield (2003),
A study of cleaning procedures used for foraminiferal Mg/Ca paleothermometry, Geochem.
Geophys. Geosyst., 4(9), 8407 doi:10.1029/
2003GC000559.
Bé, A. W. H. (1960), Ecology of recent planktonic foraminifera: part 2: Bathymetric and
seasonal distributions in the Sargasso Sea off
Bermuda, Micropaleontology, 6, 373 – 392.
Behrenfeld, M., and P. Falkowski (1997), Photosynthetic rates derived from satellite based
chlorophyll concentration, Limnol. Oceanogr.,
42, 1 – 20.
Brock, J. C., C. R. McClain, D. M. Anderson,
W. L. Prell, and W. W. Hay (1992), Southwest monsoon circulation and environments
of recent planktonic foraminifera in the
northwestern Arabian Sea, Paleoceanography,
7, 799 – 813.
Broecker, W. S., and E. Clark (1999), Carbonate size fractions: A paleocarbonate ion
proxy, Paleoceanography, 14, 596 – 604.
Broecker, W. S., and E. Clark (2001a), An evaluation of Lohmann’s foraminifera weight dissolution index, Paleoceanography, 16, 431 –
434.
Broecker, W. S., and E. Clark (2001b), Glacialto-Holocene redistribution of carbonate ion in
the deep sea, Science, 294, 2152 – 2155.
Broecker, W. S., and E. Clark (2003), Glacialage deep sea carbonate ion concentrations,
Geochem. Geophys. Geosyst., 4(6), 1047,
doi:10.1029/2003GC000506.
Brown, S. J., and H. Elderfield (1996), Variations
in Mg/Ca and Sr/Ca ratios of planktonic foraminifera caused by postdepositional dissolution: Evidence of shallow Mg-dependent
dissolution, Paleoceanography, 11, 543 – 551.
Darling, K. F., M. Kucera, C. M. Wade, P. von
Langen, and D. Pak (2003), Seasonal distribution of genetic types of planktonic foraminifer
morphospecies in the Santa Barbara Channel
and its paleoceanographic implications, Paleoceanography, 18(2), 1032, doi:10.1029/
2001PA000723.
Dekens, P. S., D. W. Lea, D. K. Pak, and H. J.
Spero (2002), Core top calibration of Mg/Ca in
tropical foraminifera: Refining paleotemperature estimation, Geochem. Geophys. Geosyst.,
3(4), 1022, doi:10.1029/2001GC000200.
de Villiers, S. (2003), Dissolution effects on foraminiferal Mg/Ca records of sea surface temperature in the western equatorial Pacific,
Paleoceanography, 18(3), 1070, doi:10.1029/
2002PA000802.
Duplessy, J.-C., A. W. H. Bé, and P. L. Blanc
(1981), Oxygen and carbon isotope composition and biogeographic distribution of planktonic foraminifera in the Indian Ocean,
Palaeogeogr. Palaeoclimatol. Palaeoecol.,
33, 9 – 46.
Elderfield, H., and G. Ganssen (2000), Reconstruction of temperature and d 18O of surface
ocean waters using Mg/Ca of planktonic foraminiferal calcite, Nature, 405, 442 – 445.
Elderfield, H., M. Vautravers, and M. Cooper
(2002), The relationship between shell size
and Mg/Ca, Sr/Ca, d18O, and d 13C of species
of planktonic foraminifera, Geochem. Geophys. Geosyst., 3(8), 1052, doi:10.1029/
2001GC000194.
Emerson, S., and M. Bender (1981), Carbon
fluxes at the sediment-water interface of the
deep sea: Calcium carbonate preservation,
J. Mar. Res., 39, 139 – 162.
Fairbanks, R., and P. Wiebe (1980), Foraminifera
and chlorophyll maximum: Vertical distribution, seasonal succession, and paleoceanographic significance, Nature, 1524 – 1525.
Fairbanks, R. G., M. Sverdlove, R. Free, P. H.
Wiebe, and A. W. H. Be (1982), Vertical distribution and isotopic fractionation of living
planktonic foraminifera from the Panama Basin, Nature, 298, 841 – 844.
Farmer, E. C., A. Kaplan, P. B. deMenocal, and
J. Lynch-Stieglitz (2007), Corroborating ecological depth preferences of planktonic foraminifera in the tropical Atlantic with the stable
oxygen isotope ratios of core top specimens,
Paleoceanography, 22, PA3205, doi:10.1029/
2006PA001361.
Fehrenbacher, J., P. A. Martin, and G. Eshel
(2006), Glacial deep water carbonate chemistry inferred from foraminiferal Mg/Ca: A case
study from the western tropical Atlantic, Geochem. Geophys. Geosyst., 7, Q09P16,
doi:10.1029/2005GC001156.
Hastings, D., A. Russell, and S. R. Emerson
(1998), Foraminiferal magnesium in Globigerinoides sacculifer as a paleotemperature proxy,
Paleoceanography, 13, 161 – 169.
Hemleben, C., M. Spindler, I. Breitinger, and
W. G. Deuser (1985), Field and laboratory
studies on the ontogeny and ecology of some
globorotaliid species from the Sargasso Sea
off Bermuda, J. Foraminiferal Res., 15,
254 – 272.
Kipp, N. (1976), New transfer function for estimating past surface conditions from seabed
distribution of planktonic foraminiferal assemblages in the North Atlantic, in Investigation of
Late Quaternary Paleoceanography and Paleoclimatology, edited by R. Cline and J. Hays,
Mem. Geol. Soc. Am., 145, 3 – 42.
Kroon, D., and K. Darling (1995), Size and upwelling control of the stable isotope composit i o n o f N e o g l o b o q u a d r i n a d u t e r t re i
(d’Orbigny), Globigerinoides ruber (d’Orbigny)
and Globigerina bulloides d’Orbigny: Examples
from the Panama Basin and the Arabian Sea,
J. Foraminiferal Res., 25, 39 – 53.
Kucera, M., and K. Darling (2002), Cryptic species of planktonic foraminifera: Their effect on
paleoceanographic reconstructions, Philos.
Soc. Trans. London, Ser. A, 360, 695 – 718.
Le, J., and N. J. Shackleton (1992), Carbonate
dissolution fluctuations in the western equatorial Pacific during the Late Quaternary, Paleoceanography, 7, 21 – 42.
Lea, D. W., T. A. Mashiotta, and H. J. Spero
(1999), Controls on magnesium and strontium
uptake in planktonic foraminifera determined
by live culturing, Geochim. Cosmochim. Acta,
63, 2369 – 2379.
Lea, D., D. K. Pak, and H. Spero (2000), Climatic impact of the late Quaternary equatorial
Pacific sea surface temperature, Science, 289,
1719 – 1724.
Lear, C. H., Y. Rosenthal, and N. Slowey (2002),
Benthic foraminiferal Mg/Ca paleothermometry: A revised core top calibration, Geochim.
Cosmochim. Acta, 66, 3375 – 3387.
Locarnini, R. A., A. V. Mishonov, J. I. Antonov,
T. P. Boyer, and H. E. Garcia (2006), World
Ocean Atlas 2005, vol. 1, Temperature [CDROM], edited by S. Levitus, NOAA Atlas NESDIS, vol. 61, 182 pp., NOAA, Silver Spring, Md.
Loubere, P. (2001), Nutrient and oceanographic
changes in the eastern equatorial Pacific from
the last full glacial to the present, Global Planet. Change, 29, 77 – 98.
11 of 12
PA3217
Marchitto, T. M., J. Lynch-Stieglitz, and
S. Hemming (2005), Deep Pacific CaCO 3
compensation and glacial-interglacial atmospheric CO2, Earth Planet. Sci. Lett., 231,
317 – 336.
Mashiotta, T. A., D. W. Lea, and H. J. Spero
(1999), Glacial-interglacial changes in subantarctic sea surface temperature and d18O-water
using foraminiferal Mg, Earth Planet. Sci.
Lett., 170, 417 – 432.
McConnell, M., and R. C. Thunell (2005), Calibration of the planktonic foraminiferal Mg/Ca
paleothermometer: Sediment trap results from
the Guaymas Basin, Gulf of California, Paleoceanography, 20, PA2016, doi:10.1029/
2004PA001077.
Mekik, F., and R. François (2006), Tracing deep
sea calcite dissolution: Globorotalia menardii
fragmentation index and elemental ratios (Mg/
Ca and Mg/Sr) in planktonic foraminifers, Paleoceanography, 21, PA4219, doi:10.1029/
2006PA001296.
Mekik, F. A., P. W. Loubere, and D. E. Archer
(2002), Organic carbon flux and organic carbon to calcite flux ratio recorded in deep-sea
carbonates: Demonstration and a new proxy,
Global Biogeochem. Cycles, 16(3), 1052,
doi:10.1029/2001GB001634.
Mekik, F., P. Loubere, and M. Richaud (2007),
Rain ratio variation in the tropical ocean: Tests
with surface sediments in the eastern equatorial Pacific, Deep Sea Res., Part II, 54, 706 –
721, doi:10.1016/j.dsr2.2007.01.010.
Norris, R., R. Cortfield, and J. Cartlidge (1996),
What is gradualism? Cryptic speciation in Globorotaliid foraminifera, Paleobiology, 22(3),
386 – 405.
Nürnberg, D. (1995), Magnesium in tests of Neogloboquadrina pachyderma sinistral from high
northern and southern latitudes, J. Foraminiferal Res., 25, 350 – 368.
Nürnberg, D., J. Bijma, and C. Hemleben (1996),
Assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass
temperatures, Geochim. Cosmochim. Acta,
60, 803 – 814.
Oppo, D., and R. Fairbanks (1989), Carbon isotope composition of tropical surface water during the past 22000 years, Paleoceanography,
4, 333 – 351.
Regenberg, M., D. Nürnberg, S. Steph, J. Groeneveld,
D. Garbe-Schönberg, R. Tiedemann, and W.-C.
Dullo (2006), Assessing the effect of dissolution on planktonic foraminiferal Mg/Ca ratios:
Evidence from Caribbean core tops, Geochem.
Geophys. Geosyst., 7, Q07P15, doi:10.1029/
2005GC001019.
Rosenthal, Y., and G. P. Lohmann (2002), Accurate estimation of sea surface temperatures
using dissolution-corrected calibrations for
Mg/Ca paleothermometry, Paleoceanography,
17(3), 1044, doi:10.1029/2001PA000749.
Rosenthal, Y., E. A. Boyle, and N. Slowey
(1997), Environmental controls on the incorporation of Mg, Sr, F and Cd into benthic
foraminifera shells from Little Bahama
Bank: Prospects for thermocline paleoceanography, Geochim. Cosmochim. Acta, 61,
3633 – 3643.
Rosenthal, Y., P. M. Field, and R. M. Sherrell
(1999), Precise determination of element/calcium ratios in calcareous samples using sector
field inductively coupled plasma mass spectrometry, Anal. Chem., 71, 3248 – 3253.
Rosenthal, Y., G. P. Lohmann, K. C. Lohmann,
and R. M. Sherrell (2000), Incorporation and
preservation of Mg in G. sacculifer: Implications for reconstructing sea surface tempera-
PA3217
MEKIK ET AL.: Mg/Ca DISSOLUTION CORRECTION
tures and the oxygen isotopic composition of
sea water, Paleoceanography, 15, 135 – 145.
Rosenthal, Y., et al. (2004), Interlaboratory comparison study of Mg/Ca and Sr/Ca measureme nts in p la nkt onic f or ami nif er a for
paleoceanographic research, Geochem. Geophys. Geosyst., 5, Q04D09, doi:10.1029/
2003GC000650.
Schiebel, R., J. Bijma, and C. Hemleben (1997),
Population dynamics of the planktic foraminifer Globigerina bulloides from the eastern
North Atlantic, Deep Sea Res., Part I, 44,
1701 – 1713.
Schmidt, G. A., and S. Mulitza (2002), Global
calibration of ecological models of planktic
foraminifera from core top carbonate oxygen18, Mar. Micropaleontol., 44, 125 – 140.
Schweitzer, P. N., and G. P. Lohmann (1991),
Ontogeny and habitat of modern menardii
from planktonic foraminifera, J. Foraminiferal
Res., 21, 332 – 346.
Thiede, J. (1983), Skeletal plankton and nekton
in upwelling water masses off northwestern
South America and northwest Africa, in
Coastal Upwelling, edited by E. Suess and
J. Thiede, pp. 183 – 207, Plenum, New
York.
van Leeuwen, R. J. W. (1989), Sea-floor distribution and late Quaternary faunal patterns of
planktonic and benthic foraminifera in the
12 of 12
PA3217
Angola Basin, Utrecht Micropaleontol. Bull.,
38, 1 – 288.
Zhang, J. (1985), Living planktonic foraminifera
from the eastern Arabian Sea, Deep Sea Res.,
Part A, 32, 789 – 798.
R. François and M. Soon, Department of
Earth and Ocean Sciences, University of British
Columbia, Vancouver, B. C., Canada.
F. Mekik, Department of Geology, Grand
Valley State University, Allendale, MI 49401,
USA. (mekikf@gvsu.edu)