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Seawater Recharge Into Oceanic Crust:
IODP Exp 327 Grizzly Bare
C. Geoffrey Wheat1, Samuel Hulme2, Andrew Fisher3,
Beth N. Orcutt4
and Cowen, Becker, ………others ????
To be submitted to EPSL
Last update: Sept 4, 2011
1
Global Undersea Research Unit, University of Alaska Fairbanks, PO Box 475, Moss Landing,
CA, 95039, 831-633-7033, wheat@mbari.org
2
Moss Landing Marine Laboratory, Moss Landing, CA, 95039, 831-359-1907,
samiam0101@gmail.com
3
University of California Santa Cruz, Santa Cruz, CA, 831-459-5598, afisher@ucsc.edu
4
Center for Geomicrobiology, Aarhus University, Aarhus, 8000 Denmark,
beth.orcutt@biology.au.dk
Wheat et al. Results from Site 1363
Page 1
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47
Abstract (150 words)
Systematic variations in upper basement temperatures and chemical profiles of
48
pore waters from Integrated Ocean Drilling Program Site 1363 document mixing and
49
reaction within the basaltic crust adjacent to Grizzly Bare outcrop, a 3.6 m.y-old site of
50
seawater inflow to the ocean crust. A transect of seven holes was established ~50 m to
51
~750 m from the outcrop, providing samples and data that elucidate the extent of
52
alteration, mixing, and partitioning of fluids within the uppermost basaltic crust. Upper
53
basement temperatures increase from ~6°C to >40 °C with increasing distance from Grizzly
54
Bare outcrop. The concentrations of major ions in pore fluids at the sediment-basement
55
contact are generally consistent with mixing between seawater and altered basement fluids
56
collected other ocean drilling basement boreholes and seeping from Baby Bare outcrop,
57
located ~45 to 52 km to the north. Reactions within upper basement affect a range of ions
58
(Mn, Fe, Mo, Si, phosphate, V, and U) all of which are reactive in sediment. The apparent 14C
59
age of basal pore fluids is similar to that determined for fluids sampled from ODP Hole
60
1026B and Baby Bare outcrop, much older than bottom seawater, and have a negative  13C,
61
indicating a diagenetic influence and exchange with overlying sediment pore waters.
62
Collectively, these results are consistent with the hypothesis that hydrothermal fluids
63
recharge at Grizzly Bare outcrop and subsequently travel north towards Baby Bare
64
outcrop, with extensive mixing between younger and older basement fluids soon after
65
recharge.
66
Wheat et al. Results from Site 1363
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1. Introduction
The eastern flank of the Juan de Fuca ridge has been the target of mapping, heat flow,
69
sediment coring, seismic, submersible expeditions, and scientific drilling (ODP Leg 168 and
70
IODP Exp 301 and 327; Davis et al., 1997; Fisher et al., 2005 and 2011). The central theme of
71
these studies is to elucidate the coupled hydrogeologic, geochemical, and microbiological
72
processes and properties within a hydrogeologic system in a ridge flank setting, where fluids,
73
heat, and solute fluxes are driven by lithospheric cooling and focused by basaltic basement
74
roughness and sediment accumulation (e.g., Fisher and Wheat, 2010). There are four basement
75
outcrops located ~100 km east of the active spreading center on the Juan de Fuca Ridge at 47°N.
76
These outcrops reside on 3.5-3.6 Ma seafloor, surrounded by sediment (mostly turbidites) that is
77
250 to 600 m thick (Davis et al., 1992; Underwood et al., 2005) (Figure 1a). This regionally thick
78
sediment is orders of magnitude less permeable than the upper basaltic crust, and limits the flow
79
of seawater into and out of the crust to areas with exposed basalt at the seafloor.
80
Three of the basaltic outcrops (Baby, Mama, and Papa Bare outcrops) discharge
81
reacted basement “formation” fluids to the overlying ocean at modest rates (e.g., 2-10 l/s
82
from Baby Bare outcrop; Thomson et al., 1995; Wheat et al., 2004). The source for these
83
altered fluids is seawater that is introduced to basaltic basement without interacting with
84
sediment. This occurs to the south of these three outcrops, based on systematic variations
85
in basement fluid compositions (Wheat et al., 2000; Hulme and Wheat 2011). Grizzly Bare
86
outcrop, the fourth outcrop, rises *** m above the sediment plain ~52 km to the south-
87
southeast, where heat flow, seismic, and modeling studies indicate that cold seawater
88
enters the basaltic crust (Fisher et al., 2003; Hutnak et al., 2006). Thus flow within
89
basement is consistent with a northeastern direction, perhaps in part because of the
Wheat et al. Results from Site 1363
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tectonic and structural fabric of the crust that imparts azimuthal anisotropy in crustal
91
permeability (Wheat et al., 2000; Fisher et al., 2008). Along the flow path seawater warms
92
quickly based on surficial heat flow measurements that project to a temperature of ~30°C
93
in upper basement only 500 m from exposed basalt and where sediment is 230 m thick. As
94
this fluid warms, it reacts with basalt and exchanges, via diffusion, with overlying sediment
95
pore water. Transport and chemical and thermal exchange continues within the crust for
96
tens to hundreds of years, producing a fluid that is depleted in dissolved oxygen and
97
nitrate, nearly depleted in magnesium and gaining Ca and heat (64°C) before it discharges
98
at the three outcrops (Elderfield et al., 1999; Wheat and Mottl, 2000).
99
Seven boreholes at four distances from exposed basalt were cored on the
100
northeastern flank of Grizzly Bare outcrop during Integrated Ocean Drilling Program
101
(IODP) Expedition 327 at Site 1363 (Figure 1B; Fisher et al., 2011). These four locations
102
result in a transect that was designed to elucidate thermal, chemical, and microbial
103
conditions within uppermost basaltic basement, thus documenting reaction and exchange
104
within the inlet portion of a ridge flank hydrothermal system (RFHS). Ideally changes in the
105
chemical composition reflect the kinetics of reaction and the residence time of fluids within
106
basement, presumably following a path of chemical and thermal change similar to that
107
documented at IODP Hole 1301A (Wheat et al., 2010). Pore water data from these cored
108
boreholes are the first that document processes within the inlet portion of a RFHS and
109
provide a measure of the spatial, and by extrapolation temporal, characteristics of change
110
reflecting reaction and transport processes.
111
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2. Methods and Results
Wheat et al. Results from Site 1363
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Of the seven boreholes drilled at Site 1363, three were washed through the sediment
114
section without recovering material and basement was tagged. This procedure allowed us to
115
determine the sediment thickness. The ship was then offset ~10 m and a second hole was cored
116
with the goal of recovering sediment close to the sediment-basalt interface with the advanced
117
piston corer (APC) system, which typically does a better job of preserving sediment than the
118
extended core barrel system (XCB). Yet, both systems were used to core sediment, because the
119
XCB system recovered more intact material from sandy horizons. Only the XCB system was
120
used to core the upper portion of the basaltic crust in two holes (1363B and D).
121
Eight thermal measurements were made in these holes to confirm the temperature of the
122
sediment-basalt interface that was estimated from surface heat flow measurements with a 2-m-
123
long probe (Fisher et al., 2011) (Table 1). Temperatures at the basement interface increase
124
monotonically with distance from exposed outcrop and sediment thickness with a crustal
125
temperature of ##°C only ### m from the outcrop in an area where the regional
126
temperature is ~64°C. DUDE
127
Sediment pore waters were extracted by squeezing cored sediment that was processed
128
within a nitrogen-filled glovebag at room temperature (Fisher et al., 2011). Analytical results for
129
determining pore water composition using standard colorimetric, titration, inductive coupled
130
plasma (ICP) emission and mass spectrometery, and ion chromotraphy techniques are tabulated
131
(Fisher et al., 2011), except for the carbon isotopic measurements which were made on four 30-
132
to 60-ml samples sealed in glass bottles and poisoned with mercuric chloride (Table 1 and 2).
133
These measurements were made at the National Ocean Sciences Accelerator Mass Spectrometry
134
Facility from the dissolved inorganic carbon in the samples. These samples were taken close to
135
the base of the sediment column, but not as close as other pore water samples.
Wheat et al. Results from Site 1363
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Sediment pore water chemical profiles are shaped by diagenetic reactions and exchange
137
with basement formation fluids as observed at Ocean Drilling Program (ODP) Sites 1026 and
138
1027 and IODP Site 1031 (Davis et al., 1997; Fisher et al., 2005). However, in contrast to these
139
sites, pore waters from the base of the sediment column at IODP Site 1363 are cooler and
140
typically less altered (Table 1, Figure 2). For example, Mg concentrations decrease downcore,
141
approaching values in the range of 36 to 28 mmol/kg. Sulfate reduction in the sediment column
142
results in an increase in alkalinity, both showing an apex about half way down the sediment
143
column. At the base of the sediment column sulfate and alkalinity trend towards bottom seawater
144
values in response to exchange with a less altered fluid in basement. Concentrations of Ca
145
generally increase downcore, with the exception of the profile affected by carbonate precipitation
146
resulting from the high alkalinity produced by microbial sulfate reduction. Other elements, such
147
as K and Rb, show changes in the pore water concentrations with depth terminating near the
148
sediment-basement contact at a concentration that is generally altered relative to seawater.
149
Because of the K sampling artifact from squeezing (de Lange et al., 1992), we reduced the
150
concentration by 1.4 mmol/kg for all values in Figure 2 and Table 1.
151
The composition of the basement fluid was calculated using a linear extrapolation of the
152
deepest four to ten samples to the depth of uppermost basement for holes 1363B, D, and F. This
153
analysis is adequate for most chemical species (Wheat et al., 2004). The number of samples used
154
for these extrapolations differed from hole to hole and with ionic species, reflecting the reactivity
155
of the ion and the shape of the profile. Because the deepest sample from Hole 1363G was
156
collected at the interface and gradients are generally steep, we used the composition of this fluid
157
as the fluid composition in basement. This composition is consistent with the average of all of
158
samples collected at a “curation” depth greater than 18 m. These “deeper” samples are assumed
Wheat et al. Results from Site 1363
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to be a uniform slurry that was sucked into the core liner during the piston coring process.
160
Because the compositions of these slurry samples match those from the sample collected at 17.5
161
m depth and the 17.5 m depth sample fits pore water trends, the slurry samples appear to be
162
chemically representative of basal pore water conditions.
163
164
3. Discussion
165
3.1. Transport
166
The prevailing paradigm of RFHS is that as seawater enters the basement it warms,
167
reacts with basalt, is affected by microbial processes, and exchanges with overlying
168
sediment pore waters. Thus, the temperature of the basement fluid is affected by transport
169
processes, which include advection and diffusion, whereas the fluid composition is affect by
170
transport and reaction processes. If transport processes alone control the composition of
171
basement fluids near Grizzly Bare, then one might expect a linear trend between the
172
temperature and Mg concentration at the sediment-basement interface be defined by
173
bottom seawater and Baby Bare springs (Figure 3A). This trend is likely because laboratory
174
seawater-basalt experiments at low temperatures (25°C) illustrate that little change in the
175
fluid composition occurs during a 1.3-year-long study (Seyfried, 1977), consistent with the
176
global data set (Fisher and Wheat, 2010). Thus if mixing occurs rapidly (years) then
177
reaction will likely not have an affect on Mg concentrations. Holes 1363C/D lie on this
178
mixing trend, suggesting that advective transport and conservative mixing are affective
179
within hundreds of meter from the basaltic outcrop. However, data from the other holes
180
(1363 B, F, and G) closer to the outcrop fall below this line, indicating either a preferential
181
loss of heat or Mg. The loss of Mg is not likely, based on experiment and environment data.
Wheat et al. Results from Site 1363
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In contrast, the loss of heat is likely. Heat and fluid composition are often decoupled in
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basaltic crust on ridge flanks after the basement aquifer is perturbed by drilling operations,
184
because the diffusion of heat is orders of magnitude greater than the diffusion of ions
185
(Wheat et al., 2003; Wheat et al., 2010). This non-linear relationship is consistent with cold
186
seawater downwelling into the crust well below the sediment-basement interface (Figure
187
3B). This cold fluid mines heat from the overlying warmer, less dense and altered fluid
188
derived from areas away from the outcrop. Mixing must be vigorous, because this
189
diffusional mining of heat is not evident at Hole 1363C/D. This result suggests that the fluid
190
composition within basaltic basement is stratified near the outcrop and homogeneous, at
191
least within the upper several hundred meters of permeable basaltic crust, away from the
192
outcrop. Therefore, it is conceivable that the upper basaltic basement is anoxic, similar to
193
64°C fluids from Baby Bare springs, with oxic seawater below, thus defining a potential
194
redox gradient within basement that could partition and concentrate microbial
195
populations, Such partitioning and concentration is evident near the sediment-basalt
196
interface where redox boundaries exist (Engelen et al., 2010).
197
198
Andy modeling or reference to model simulations in other papers. Thoughts???
3.2. Reaction
199
The extent of reaction within basaltic basement is assessed by comparing the fluid
200
composition in upper basement to a mixing trend defined by spring fluids from Baby Bare
201
and seawater. If mixing processes are dominant, as noted above, then data for a chemical
202
species verse Mg should lie on a mixing line. Such trends are evident for some ions (Figure
203
4), but others fall off the trend, indicating that reactive processes are important in
204
controlling fluid concentrations for those elements. Probable reactions that take place are
Wheat et al. Results from Site 1363
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assessed by comparing the results with several data sets: (1) water-rock experiments
206
(Seyfried, 1977; Seyfried and Bischoff, 1979), (2) estimated fluid compositions for upper
207
basement at ODP Sites 1023-1025 with temperatures (15-39°C) that overlap those from
208
IODP Site 1363 and ODP Sites 1028 and 1029 (Elderfield et al., 1999), (3) recovery of IODP
209
Hole 1301A after drilling disturbances (Fluids changed from a seawater composition to one
210
that is similar to springs on Baby Bare outcrop, indicative of mixing, conductive heating,
211
and reaction; Wheat et al., 2010), and (4) basal sediment pore water gradients that provide
212
a measure of exchange that affects concentrations in basement fluids for some elements
213
(e.g., Elderfield et al., 1999; Wheat et al., 2000; Hulme and Wheat, 2011).
214
The Ca-Mg data generally lie on the mixing line between Baby Bare spring fluids and
215
seawater (Figure 4). While Site 1363 data could result solely from mixing, the experimental
216
and ODP Site data have no such constraints. The linear trend for these data is consistent
217
with a “steady state” condition in which the removal of Mg from seawater is balanced by Ca
218
production, thus maintaining charge balance. The ODP data suggest a thermal control,
219
given 14C ages that are greater than 11K years, thus these fluids should be “equilibrated”
220
with basalt. Possible diffusive exchange with overlying sediment pore fluids for these two
221
elements appears to be insignificant because the borehole data that are present are not
222
linked hydrologically. The time scale for these reactions to reach a steady state exceeds
223
years, based on the Mg and temperature plot, because neither the 25°C nor the 70°C
224
experiments reached equilibrium within 1.5 and 0.5 years, respectively (Figure 3A).
225
Similarly, Mg and temperature were not conservative during the three-year period prior to
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borehole hydrologic condition returning to a pre-drilling state, but in this case of Hole
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1301A heat was added to solution instead of removed from solution at Site 1363.
Wheat et al. Results from Site 1363
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The alkalinity-Mg data from Site 1363 tend towards the mixing line, suggesting mixing
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processes near the outcrop are an important control of the alkalinity. Preferential removal
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of alkalinity is suggested by most values residing below the line and the experiment data
231
show depletions in CO2 while Mg concentrations remain relatively high indicating the
232
kinetics of reactions are quicker for the removal of alkalinity than Mg.
233
Similarly, Site 1363 K-Mg data from sites with temperatures that are less than ~30°C lie
234
on the mixing line, suggesting minimal reaction relative to mixing. The experimental and
235
field data also follow this trend, suggesting some relationship between Mg and K, yet none
236
has been proposed. However above ~30°C, K is removed relative to Mg, possibly owning to
237
a greater sediment influence. Likewise Site 1363 Li-Mg data (not shown), with the
238
exception of Hole 1363 G which has a high sediment Li concentration, are linear and lie on
239
the mixing line.
240
Sulfate concentrations in ridge lank hydrothermal systems can be explained by the
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integrated diffusive loss to the overlying pore waters with minimal removal in basaltic
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basement by microbial processes (Elderfield et al., 1999; Lever et al., 2011). Because of
243
this diffusive control, the ODP data are not expected to fall on the mixing line, and curiously
244
enough the Site 1363 data do not fall on this line. This evidence suggests that the altered
245
seawater from Hole 1363 C/D is “local” with little influence from diffusive loss of sulfate to
246
the overlying sediment and not from the area around Baby Bare. Thus, at some position
247
near the outcrop the fluid must be fully evolved with respect to thermally controlled
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elements, but the distance from the outcrop is not known given uncertainties in local
249
mixing; however, thermal data indicate that temperatures reach 60°C ** m from the
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outcrop, only ** meters from Hole 1363 C/D.
Wheat et al. Results from Site 1363
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Mn-Mg data from Site 1363 lie above the mixing line, as do the other environmental
252
data and the 70°C experimental data. The experimental data and data from Hole 1301A
253
indicate that Mn is one of the more reactive elements within basaltic crust with a ‘steady
254
state” concentration being reached rather quickly. This concentration is much less than
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that from extrapolated data in Figure 4. These elevated Mn values are influenced by the
256
sediment and are presumed to be extremes, given the large concentration gradients near
257
the sediment-basalt interface. Likewise Mo and ammonium (and Si and Fe; not shown) data
258
appear to be influenced from sediment pore waters.
259
One of the intents of sampling close to the sediment-basalt interface was to document a redox
260
change, as evident in decreasing nitrate concentrations, in the basement formation fluid with
261
distance from the outcrop. The hope was that nitrate gradients near the sediment-basalt interface
262
were less than those at the sediment-water interface, which are typically depleted at a depth of 20
263
cm (RetroFlux expedition). We were unable to document nitrate gradients in the basal sediment
264
to a fluid with appreciable nitrate, presumably because we were unable to get samples close
265
enough to the sediment-basalt interface or a general lack of nitrate in these reacted fluids. A
266
borehole observatory (CORK) is needed to ascertain the redox condition of upper basement at
267
this site. Therefore, the nitrate data are consistent with nitrate being consumed in the basal
268
sediment/upper basement at rates that alter concentrations from those calculated from mixing
269
alone. Likewise phosphate, V, and U (not shown) are preferentially consumed.
270
3.3. Residence Time
271
Four 30 to 60 ml pore water samples were analyzed for their 14C age. As with the other
272
chemical data, we used these data to extrapolate to the 14C age of the fluid in upper basaltic
273
basement, assuming that the alkalinity is a measure of DIC dilution of the endmember with the
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added C from depleted 14C from basal sediment. Although the 14C of the individual samples
275
shows a monotonic change (older) away from the outcrop, when the values are adjusted for
276
dilution with diageneic DIC, the monotonic trend vanashes. Surprising, the 14C age of these
277
fluids is tens of thousands of years, similar to values from the ODP sites and boreholes
278
(Elderfield et al., 1999; Walker et al., 2007). These relatively old 14C ages contrast with values
279
determined for pore fluids recovered near Dorodo outcrop, a site of suspected extensive fluid
280
seepage in a much more vigorous ridge-flank hydrothermal setting (Wheat and Fisher, 2010).
281
The 13C for the fluid in upper basaltic basement was similarily calculated. For this case
282
we assumed a diagenetic 13C of -20‰, consistent with a plankton/sediment source (McCorkle et
283
al., 1985; Rau et al., 2001; Zeebe, 2007). The calculated values range from -2‰ to -12‰ without
284
a systematic trend with distance from the outcrop These values span those observed by Sansone
285
et al (1998) who analyzed spring fluids from Baby Bare outcrop with seawater 13C and Walker
286
et al. (2007), who analyzed borehole fluids from 1026B and harpoon fluids from Baby Bare
287
outcrop with 13C values reflecting diagenetic inputs. The spring fluids from Baby Bare are
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devoid sediment artifacts (e.g., excess ammonium and dissolved silica), whereas borehole fluids
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from Hole 1026B have a “sediment” contamination (Wheat et al., 2004). Data to determine if
290
sediment influences results from the Baby Bare harpoon were not provided. Walker et al. (2007)
291
suggest that the more negative 13C results from the almost complete removal of seawater during
292
subsurface precipitation of carbonate and the addition of basaltic carbon. Alternatively, diffusive
293
exchange with sediment pore waters could be the source of the lighter 13C.
294
Nevertheless, the carbon isotopic story is complex and does not follow those elements
295
that are controlled by diffusive exchange with overlying pore water (e.g., sulfate) or reaction
296
with basalt (e.g., Mg). The complete data set and in particular the two types of isotopic C data
Wheat et al. Results from Site 1363
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highlight the complex mixing scenario at the inlet of a ridge flank hydrothermal system, yet the
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isotopic DIC data as a whole remain confused. For example, many ions show systematic trends,
299
reflecting reaction and diffusive processes that are modulated by advective transport and mixing.
300
Ions that do not follow these trends are thought to be highly reactive. Given the limited data, it
301
appears that DIC falls in the category of highly reactive ions. This result is not anticipated
302
because pore water gradients near the sediment-basalt in general are much smaller than those of
303
other ions that react in a systematic way and carbonate precipitation is ubiquitous and relatively
304
quick in an environment where Ca, alkalinity, and temperature are systematic. Thus, the two
305
basic modes of transport cannot explain the ranges in DIC isotopic values (Sansone et al., 1998;
306
Elderfield et al., 1999; Walker et al., 2007; this work) and a highly reactive DIC pool is not
307
consistent with systematic alkalinity values nor microbial rates (Lever et al., 2010): additional
308
studies are required to sort out the DIC story.
309
Conclusions
310
We present new pore water data from IODP Site 1363 at the base of Grizzly Bare
311
Seamount, a site where seawater flows into the crust. Prior to this study we envisioned a
312
“conveyor belt” of chemical and thermal change as bottom seawater enters basaltic basement and
313
is transported to sites of seepage at the seafloor tens of kilometers away. Instead, we find highly
314
altered fluids with a warm (64ºC) chemical signature within a hundred meters of the basaltic
315
outcrop and chemical and thermal evidence pointing to a stratified fluid composition in upper
316
basaltic basement close to the seamount yet is well mixed only 800 m from the outcrop. Such
317
complexity at outcrops is observed in computer simulations of fluid transport and brings to bare
318
the idea that the fluid composition is likely stratified here with several potential redox (e.g.,
319
reducing-oxic-reducing) gradients in a setting that is much warmer than bottom seawater. Such
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gradients are ideally suited to spur microbial activity, suggesting that the greatest density of
321
microbial activity in ridge flank basaltic crust occurs within hundreds of meters of seamounts. A
322
multi-level borehole observatory (CORK) is required to test this hypotheses.
323
Our results do not preclude a “converyor belt” scenario. The transect was chosen because
324
it was located on a seismic line that is roughly parallel to the active spreading center to the west,
325
in line with outcrops and borehole observatories (CORKs) to the north northeast. However,
326
thermal data from a seismic line to the east southeast present a more compelling decrease in heat
327
flow near the outcrop, signifying greater recharge should happen along this seismic line. Such
328
findings place more interest in studying the hydrologic system of seamounts and outcrops.
329
Acknowledgements
330
This work was made possible through the Integrated Ocean Drilling Program and the
331
dedicated personnel that make it possible to collect quality deep-sea sediment cores. Shore-based
332
funding was provided from the U.S. Science Support Program and the Center for Dark Energy
333
Biosphere Investigations (C-DEBI) . C-DEBI contribution ***.
334
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Figure Captions
Figure 1 map of general area nad of griz with core locations
Figure 2 chem as a function of depth
Figure 3 vs mg versus temp and drawing of flow
Figure 4 ions vs mg
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Table 1. Composition of fluids in basaltic basement at ODP Site U1363 and Baby Bare outcrop
compared to the composition of bottom seawater.
Latitude (N)
Longitude (W)
Distance from outcrop (m)
Sediment Thickness (m)
Deepest Pore Water (m)
Basement Temp (°C)
Mg (mmol/kg)
Chlorinity (mmol/kg)
Sulfate (mmol/kg)
Alkalinity (mmol/kg)
Br (mmol/kg)
pH
Na (mmol/kg)
Na/Cl (mol/mol)
Ca (mmol/kg)
Sr (mmol/kg)
Ba (mmol/kg)
K (mmol/kg)
Li (mmol/kg)
Rb (mmol/kg)
Cs (nmol/kg)
Si (mmol/kg)
B (mmol/kg)
Nitrate (mmol/kg)
Ammonium (mmol/kg)
Phosphate (mmol/kg)
Mn (mmol/kg)
Fe (mmol/kg)
V (nmol/kg)
U (nmol/kg)
Mo (nmol/kg)
 13C
14
C age (years)
Bottom 1
Seawater
1363G 2,3
1363F 2
1363B 2
1363C/D 2
Baby 1
Bare
----------1.8
52.6
542
28.1
2.5
--7.9
467
0.861
10.3
86
0.15
10.1
26.6
1.37
2.2
190
410
39.2
0.3
2.8
0.001
0.001
38.4
12
100
-0.6
2300
47º17.312’
128º2.170’
47º17.326’
128º2.137’
47º17.352’
128º2.106’
47º17.574’
128º2.762’
47º42.37’
127º47.15’
70
17.5
17.5
6
36
544
25.2
2.67
0.82
7.2
473
0.869
21.0
85
0.35
9.2
62
1.41
2
420
460
2.5
107
2.8
55
2.7
6
4.8
870
-12
12,000
115
35.0
32.2
7
35
536
25.8
1.20
0.80
7.3
464
0.865
22.6
83
0.07
8.9
17.9
1.7
3
300
580
2
110
0.2
6
0
14
7.2
560
-4
10,000
177
57.0
53.3
12
35
546
27.3
1.71
0.79
7.3
474
0.869
23.3
90
0.59
8.5
18.2
1.33
3.1
310
450
1
170
2.0
79
0
6
1.4
550
---
400
231.2
222.7
33
28.6
551
26.7
0.98
0.81
7.1
471
0.854
35.0
101
1.04
4.6
16.7
0.53
2.2
350
270
2
220
0.5
100
3
5
2
280
-8.9
18,000
52,000
0
--64
0.98
554
17.8
0.43
--8.3
473
0.853
55.2
110
0.43
6.88
9.0
1.12
5.3
360
570
0.8
76
0.3
2.9
<0.05
10
0.6
297
-0.6
12000 4
1
Data are from Wheat and Mottl (2000), Wheat et al. (2002), and Sansone et al. (1998).
Data are from Fisher et al., 2011.
3
Samples from deeper than 17.5 meters result from the piston sucking in and homogenizing basal
sediment without further penetration even though depths are recorded as deeper than 17.5 m.
4
(Walker et al., 2007).
2
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Table 2. Measured carbon isotopic values and calculated values for the uppermost fluid in
basaltic basement.
measured measured measured endmember Endmember3 Endmember4
DIC
DIC
alkalinity alkalinity
calculated
calculated
14
13C
14C
mmol/kg
mmol/kg
C age
13C
1
U1363D 4X3
-11.46
-916.87
1.27
0.98
18000
-8.9
2A1 U1363G 3H6
-13.1
-792.69
2.91
2.67
12000
-12
1
2B U1363G 3H6
-13.11
-799.78
2.91
2.67
12000
-12
32 U1363F 4H3
-7.94
-820.72
1.81
1.20
10000
-1.8
42 U1363F 4H3
-10.92
-801.3
1.81
1.20
9400
-6.3
1
Duplicate samples.
Two separately processed samples from the same core.
3
Assumes that the alkalinity and DIC are equilivent given the pH of the pore waters.
4
Assumes that the 13C added to the formation fluid from diagenesis of the sediment is -20‰.
2
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