Can foraminifera be used as indicator of
environmental changes?
Richard Hofmann
Technische Universität Bergakademie Freiberg
Abstract. The analysis of foraminifera is a valuable utility in modern geosciences. As has been proved in the last decades, foraminifera are very usefull in
tasks of environmental research. I would like to give an overview on some
concepts, the way they work and the restriction of the applicability. In an effort to
underline the acceptation of foraminifera in detection of environmantel changes,
some examples from geological/environmental research will be given.
1. Introduction
The aim of ecological studies is to prove the relationship between the biota and the
environment. Due to the abundance and the formation of well preservable shells,
foraminifera are very useful in analysing and assessing recent and ancient marine
environments (Murray, 2002).
The ecological behavior of foraminifera depends on physical, chemical and
biological factors. The variation of any attribute, leads to a modification of
behavior, chemism and metabolism of the individual specimen respectively the
whole community. The purpose is, to attribute the change in living activities to
actual environmental variations.
2. Concepts
In order to subsume the versatile techniques in environmental research, I present
three basic concepts to conclude the environmental setting and change by the help
of the analysis of formanifera.
2
Richard Hofmann
2.1 Assemblage Analysis
These methods are based on the quantitative and qualitative analysis of
communities. Every species of foraminifera claims special demands to its
environment. By summarizing the individual preferences of each species, it is
possible to define a common ecological window for the considered attributes in
the habitat. The ecological requirements for a species are extracted from recent
studies on living specimens. Therefore, the applicability for ancient habitats
requires that the same taxa prefer identic, at least similar conditions.
Of course, the sole definition of the environmental attributes is not sufficient to
note changes. Therefore, it is necessary to sample more than one area in order to
put the differential ecological factors in spatial and temporal context.
For instance, the micropalaeontological preparation of selected slices from
sediment core yields different faunal distributions which can be used to
reconstruct the development of palaeocommunities over one profile. Otherwise,
those facies analyses could be used to distinguish sedimentary and
palaeogeographic settings within one time interval.
One of the main problems of the assemblage analysis is the distinction between
natural variability and apparent environmental change (fig. 1). For instance, the
natural variation caused by predation or seasonal fluctuations do not reflect
disturbances of the considered ecosystem.
The ocean is a 3-D living space. Therefore, it is obvious that planktic faunas are
representing other ecological attributes than benthic communities. Foraminfera
have colonized the free water column at least since the Jurassic (Oxford et al.
2002). For this reasons it is recommended to separate planktic and benthic taxa in
reference to environmental conclusions.
To avert the mixing of environmental signals, the determination of autochtonous
and allochtonous faunal components is necessary. Likewise, the redeposition of
already dead organisms, so called ghost-communities, could be lead to
misinterpretation of the environment.
Can foraminifera be used as indicator of environmental changes?
3
Fig.1. Variability and change: (A) variability of a mean without change, (B)
variability of a mean with a progressive change, (C) variability of a mean that has
longer-term cyclic variation, segments a and b appear to indicate change (redrawn
from Murray, 2000).
2.2 Measurements
Foraminifera provide amazing proxy data, by chemical analyses and
measurements. As a result of the formation of durable carbonatic shells,
foraminifera are able to conserve the predominant ratio of stable isotops of
Oxygen, Carbon and Calcium, at the time of their demise.
The most important ratio of isotopes are 18O/16O and 13C/12C. The reasons for
isotopic ratio variation are versatile (fig. 2). The palaeoecological attributes, which
can assessed by isotope ratio are palaeotemperature, palaeosalinity, or ancient
water supplies.
Also in isotope analysis, it is strongly recommended to distinguish between
planktic and benthic faunas (fig. 3). The stable isotope ratio is not constant within
the water column. Already, the difference of the water temperature from bottom
4
Richard Hofmann
waters to medium and shallow water, will have an significant influence on isotope
data in foraminiferal tests.
Fig. 2. Diagram illustrating how the stable isotopes of oxygen and carbon in
microfossil tests will tend to vary with depth and salinity. The black arrows show
the most typical isotope trends seen as environments become more extreme.
(redrawn from Armstrong & Brasier 2005).
Oxygen Isotopes (Armstrong & Brasier, 2005)
Five main factors affect the ratio between the stable isotopes of oxygen in the
carbonatic test of foraminifera. For the influence of one of these to be calculated,
the other will be need to be estimated or known.
a) isotopic composition of water
There are many factors that shift the δ18O. High evaporation rates on water surface
leads to an enrichment of 18O.
b) temperature
Carbonates, built in warm water incorporate more
cooler water.
16
O than those precipitated in
Can foraminifera be used as indicator of environmental changes?
5
c) mineral phase
Aragonitic tests contain more 18O than those composed of calcite.
d) vital effects
Due to metabolic processes, the secretion of CaCO3 in living organisms is not in
equilibrium with sea water. The amount of shift depends on the taxa and size.
e) diagenesis
The ratio could also be disturbed by meteoric waters and diagenetic fluids
Fig. 3. Fundamental differences in δ18O between benthic and planktonic
foraminifera (redrawn from Armstrong & Brasier 2005).
Carbon Isotopes (Armstrong & Brasier, 2005)
The 13C/12C-ratio is affected be several processes of isotope fraction, depletion or
enrichment.
a) surface water productivity
At high primary productivity,
atmosphere as the heavier 13C.
12
C is more likely removed from the ocean and
b) biological oxidation
The respiration of organic matter on the ocean floor and in mid-waters leads to a
re-release of 12C to the water column.
c) upwelling and mixing
Where 13C-depleted waters came up to the sea surface as by upwelling, the
common ratio will be shifted.
6
Richard Hofmann
d) carbon burial
The deposition of large amounts of organic matter means a temporal deprivation
of carbon isotopes and yields to an increase of the δ13C.
e) diagenesis
δ13C is much easily reset by meteoric and burial diagenesis than δ18O. The most
fluids tend to carry 12C.
2.3 Monitoring
These methods are particularly used in modern and subrecent environments.
The main technique consists on collecting living specimens and investigation of
the biologic and environmental behavior.
The goal is, to prove the impact of pollutants and salinity fluctuations on recent
habitats.
Foraminifera are suitable because of their short life cycle, their large numbers, and
their ability to react quickly on environmental disturbance (Coccioni, 2000).
An apparently response of foraminifera to pollutants and variations of salinity
(Geslin et al. 2000) is the development of abnormal shell architectures. Different
types of shell deformation are recognized .
Reduced shell size, aberrant chamber shape, disturbed chamber arrangement,
additional chambers, nondeveloped test and siamese twins are abundant in
stressed enironments (Coccioni, 2000; Geslin et al. 2000).
Similar to the technique of assemblage analysis (see 2.1), recent environments can
easily assessed by the foraminiferal distribution.
3. Examples
3.1 The Messinian Salinity Crisis
Blanc-Valleron et al. (2002)
A section of the Tripoli Formation (6.96 – 5.98 Ma) has been sampled for a high
resolution integrated investigation on stable isotopes of carbonate, microfossils,
and sedimentology.
The Tripoli Formation of the Central Sicilian Basin provides good records of the
environmental changes during the transition from the beginning of restrictive
circumstances to the onset of the salinity crisis of the ancient Mediterranean. The
Falconara/Gibliscemi sections are subdivided in 46 precession-controlled cycles.
Can foraminifera be used as indicator of environmental changes?
7
The workers summarized the distributional trends of the microfaunal assemblages,
the signals of carbonate stable isotopes and the sedimentary record of each cycle,
to show the transition from normal marine to hypersaline conditions.
Beside other microfossils, such as radiolarians and diatoms, foraminifera play a
significant role in this study.
The authors assumed, several steps, in which the transition had proceed.
Period 1: Large Atlantic-Mediterranean exchange. (6.96 – 6.71 Ma)
The most abundant species of foraminifera in this sequences are cosmopolitan,
subtropical forms which indicate warm water and normal saline values. Another
hint for a permanent exchange is documented by the incidental appearance of
temperate north Atlantic forms.
Period 2: increased restriction (6.71-6.29 Ma)
The presence of north Atlantic forms indicates water mass movement through the
Mediterranean gateway. Although, the onset of poorer water exchange is shown
by the composition of benthic foraminifera assemblages that indicate poorly
ventilated bottom waters.
Period 3: further restriction (6.29 Ma)
The decrease of planktic foraminfera and the disappearance of Atlantic
radialorians describe a distinct basin restriction. Furthermore, characteristic
foraminifera species for stressed environments and higher salinities are
recognized. This interval coincides with a worldwide glacio-eustatic sea level
drop.
Period 4: the isolation (<6.29 Ma)
The final isolation of the Mediterranean from the world water circulation is found
in the last cycles of the Tripoli-sequence. An evidence for hypersaline conditions
is given by the complete absence of any marine microfossils. The transition
culminates in the formation of evaporites and desiccation features recognized in
the sedimentary record.
3.2 Changing deep water sources
(Friedrich et al. 2004)
Based on planktic and benthic foraminiferal stable isotope data, a global cooling
during the Campanian/Maastrichtian has been suggested by several workers
(Clarke and Jenkyns, 1999, Huber et. al., 2002). The authors suggest that
variation of stable isotope data of benthic and planktic foraminifera reflecting
changes in the circulation patterns and water formation in the former North
Atlantic basin. Black Nose, the drilling side where the samples had extracted, was
located at a paleolatitude of ~30° North (Hay et al. 1999) and a average paleo
water depth of 1000 – 2000 m (Norris et al. 1998). Therefore, Black Nose is
8
Richard Hofmann
suitable to investigate intermediate to deep water mass movement and may be
reflect changes of ancient deep water formation site.
Under strong greenhouse conditions, oceanic circulation is driven by the sinking
of warm, saline waters in low-latitude regions under excessive evaporation.
Those waters have a characteristic isotope-ratio with high δ18O- and low δ13Cvalues.
At the high North Atlantic, the deep water formation is a result of the sinking of
dense, lower saline water. Waters like these tends to low δ18O- and high δ13Cvalues.
The benthic foraminiferal tests, found at Black Nose, records a fluctiation of these
stable isotope-ratio. To prove this assumption, grey values of the sediment has
been measured. The variation of these values seem to fit the insolation fluctuation,
generated by Milankovich cycles.
During times of higher insolation, the deep water production in the North Atlantic
was reduced as compared to cooler periods.
During times of proposed low insolation, the reduced temperatures probably led to
increased thermohaline deep water formation in the high North Atlantic.
Therefore, the authors conclude, that the ratio of stable isotope in the shells of
benthic foraminifera, represent the predominant mode circulation.
3.3 The indication of heavy metal pollution
(Coccioni 2000)
Benthic foraminiferal distribution and trace element concentration were
investigated in surface sediments of several stations from the Goro Lagoon/Italy.
The study area is suitable for studying the response of benthic foraminifera to
trace metal pollution because of the strong levels of heavy metal pollution and the
high proportion of abnormal tests.
The study is based on 47 surface grab sediment time avereged samples collecteted
in the Goro Lagoon.
The author had analysed the faunal distribution, the mode of abnormality of tests
and the concentration of trace metals. The aim was, to evaluate a correlation
between morphologic abnormalities and the grade of pollution.
Already, the living faunal distribution shows a significant influence of
environmental stress. Only eight species were identified as living. The
assemblages are largely dominated by 3 species. Therewith, the fauna fits a typical
low diversity assmeblage.
Any of the typical test deformities (fig. 5) are found in the investigated area.
Due to the high leveled pollution with a various number of trace metals (V, Ni,
Zn, Cr, Co, Pb, Cu, Hg, Th ,) a direct correlation of the percentage of abnormal
tests between the content and concentration of pollutants is not easily to show.
Although, some relations could be approved. It has been shown that the
percentage of abnormal specimens depends on lowered salinities in the Goro
Can foraminifera be used as indicator of environmental changes?
9
Lagoon. Furthermore, a clear positive correlation between concentration of Th and
the percentage of abnormalities was found.
Fig. 4. SEM photomicrographs showing examples of nondeformed and
morphological abnormalities in benthic foraminifera. (redrawn from Geslin et al.
2000).
10
Richard Hofmann
References
Armstrong H. A., Brasier M. D. (2005). Microfossils. Second Edition. Blackwell
Publishing
Blanc-Valleron, M.M., Pierre, C., Caulet, J.P., Caruso, A. ; Rouchy, J.M., Cespuglio, G.,
Sprovieri, R., Pestrea, s. & Di Stefano, E. (2002). Sedimentary, stable isotope and
micropaleontological records of the paleoceanographic change in the Messinian Tripoli
Formation (Sicily, Italy). Palaeogeography, Palaeoclimatology, Palaeoecology 185,
255-286.
Clark; L.J:, Jenkyns, H.C. (1999). New oxygen isotope evidence for long-term Cretaceous
climatic change in the Southern hemisphere. Geology 8, 699-702
Coccioni R. (2000). Benthic Foraminifera as bioindicators of heavy metal pollution.
Environmental Micropaleontology, Volume 15 of Topics in Geobiology. Kluwer
Academic/Plenum Publishers, New York. 71-103.
Friedrich O., Herrle J.O., Klößer P., Hemleben C. (2004). Early Maastrichtian stable
Isotops: changing deep water sources in the North Atlantic? Palaeogeography,
Palaeoclimatology, Palaeoecology 211, 171-184
Geslin E., Stouff V., Debany J. P., Lesourd M. (2000). Environmental variation and
foraminiferal test abnormalities. Environmental Micropaleontology, Volume 15 of
Topics in Geobiology. Kluwer Academic/Plenum Publishers, New York, 191-215
Hay, W.W., DeCONto, R.M., Wold, C.N., Wilson, K.M., Voigt, S., Schulz, M., Rossby
Wold, A., Dullo, W.C., Ronov, A.B., Balukhovsky, A.N., Söding, E. (1999)
Alternative global Cretaceouspaleogeography. In: Barrera, E., Johnson, C.C. (Eds).
Evolution of the Cretaceous Ocean-Climate System. Special Paper-Geological Society
of America, vol 332, pp.1-47. Boulder
Huber, B.T., Norrris, R.D. MacLeod, K.G., (2002) Deep-sea paleotemperature record of
extreme warmth during the Cretaceous. Geology 30, 123-126.
Murray, J.W. (2000). When does environmental variability become environmental change?
The Proxy Record of benthic Formanifera. Environmental Micropaleontology, Volume
15 of Topics in Geobiology. Kluwer Academic/Plenum Publishers, New York, 7-37.
Norris, R.D., Kroon, D., Klaus, A., et al. (1998). Proceedings of the Ocean Drilling
Program. Initial Reports, vol. 171B. Ocean Drilling Program Celloge Staion, TX, 1360
Oxford, M.J., Gregory, F.J., Hart, M.B., Henderson, A.S., Simmons, M.D. & Watkinson,
M.P. (2002). Jurassic planktonic foraminifera from the United Kingdom. Terra Nova
14, 205-209