Combined carbonate carbon isotopic and cellular ultrastructural studies of individual benthic foraminifera : method description

Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 25 (2010): PA2211, doi:10.1029/2009PA001846.Carbon isotopes of foraminiferal tests provide a widely used proxy for past oceanographic environmental conditions. This proxy can be calibrated using live specimens, which are reliably identified with observations of cell ultrastructure. Observations of ultrastructures can also be used for studies of biological characteristics such as diet and presence of symbionts. Combining biological and isotopic studies on individual foraminifera could provide novel information, but standard isotopic methods destroy ultrastructures by desiccating specimens and observations of ultrastructure require removal of carbonate tests, preventing isotope measurements. The approach described here preserves cellular ultrastructure during isotopic analyses by keeping the foraminifera in an aqueous buffer (Phosphate Buffered Saline (PBS)). The technique was developed and standardized with 36 aliquots of NBS-19 standard of similar weight to foraminiferal tests (5 to 123 μg). Standard errors ranged from ± 0.06 to ± 0.85‰ and were caused by CO2 contaminants dissolved in the PBS. The technique was used to measure δ13C values of 96 foraminifera, 10 of which do not precipitate carbonate tests. Calcareous foraminiferal tests had corrected carbon isotope ratios of −8.5 to +3.2‰. This new technique allows comparisons of isotopic compositions of tests made by foraminifera known to be alive at the time of collection with their biological characteristics such as prey composition and presence or absence of putative symbionts. The approach may be applied to additional biomineralizing organisms such as planktonic foraminifera, pteropods, corals, and coccolithophores to elucidate certain biological controls on their paleoceanographic proxy signatures.Support was provided by NSF grants OCE‐0550396 (to J.B.M.), OCE‐0551001 (to J.M.B.), and OCE‐ 0550401 (to A.E.R.)

Bottom-water deoxygenation at the Peruvian Margin during the last deglaciation recorded by benthic foraminifera

Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the Eastern Pacific Ocean indicate an extension of oxygen depleted conditions during the deglaciation but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox-proxy. A multiple regression analysis was applied to a joint dataset of living (rose Bengal stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as dependant variable. The correlation was significant (R2 = 0.82; p < 0.05) indicating that the foraminiferal assemblages are rather governed by oxygen availability than by the deposition of particulate organic matter (R2 = 0.53; p = 0.31). We applied the regression formula to four sediment cores from the northern part of the Peruvian OMZ between 3° S and 8° S and 600 m to 1250 m water depths; thereby recording oxygenation changes at the lower boundary of the Peruvian OMZ. Each core displayed a similar trend of decreasing oxygen levels since the Last Glacial Maximum (LGM). The overall [O2]BW change from the Last Glacial Maximum and the Holocene was constrained to 30 μmol/kg at the lower boundary of the OMZ, whereas at shallower depths [O2]BW was relatively stable along the deglaciation. The deoxygenation trend was time-transgressive. It commenced at the southern core, and gradually spread to deeper waters and to the northernmost core location. This pattern indicates a gradual expansion of the OMZ during the last deglaciation, as a result of increasing surface productivity in the Eastern Equatorial Pacific and decreasing advective oxygen supply to intermediate waters off Peru

Epifaunal Foraminifera in an Infaunal World: Insights Into the Influence of Heterogeneity on the Benthic Ecology of Oxygen-Poor, Deep-Sea Habitats

A reduction in dissolved oxygen availability in marine habitats is among the predicted consequences of increasing global temperatures. An understanding of past oxygenation is critical for predictions of future changes in the extent and distribution of oxygen minimum zones (OMZs). Benthic foraminifera have been used to assess changes in paleo-oxygenation, and according to prevailing thought, oxygen-poor marine benthic habitats are dominated by sediment-dwelling infaunal foraminifera, while more oxygenated environments are populated with more epifaunal taxa. However, in this study we found elevated densities of epifaunal taxa in oxygen-poor habitats. A series of 16 multicores were taken on depth transects (360–3000 m) across an OMZ in the Southern California Bight to investigate the ecology of living (rose bengal stained) benthic foraminifera. Dissolved oxygen concentrations in bottom water at sampling sites varied from 21 to 162 μmol/l. Sampling focused on bathymetric highs in an effort to collect seafloor surface materials with coarse sediments in areas not typically targeted for sampling. Mean grain size varied from about 131 (gravelly sand) to about 830 μm (coarse sand with fine gravel). Vertical distribution patterns (0–2 cm) were consistent with those of conspecifics reported elsewhere, and reconfirm that Cibicidoides wuellerstorfi and Hanzawaia nipponica have a living preference at or near the sediment-water interface. As expected, assemblages were dominated by infaunal taxa, such as Uvigerina and Bolivina, traditionally associated with the supersaturated, unconsolidated mud, characteristic of OMZ habitats, suggesting that these taxa are not sensitive to substrate type. However, despite dysoxic conditions (21–28 μmol/l), epifaunal taxa comprised as much as 36% of the stained population at the five sites with the coarsest mean grain size, while other measured environmental parameters remained relatively constant. We suggest that these epifaunal taxa, including C. wuellerstorfi, prefer habitats with coarse grains that allow them to remain at or above the sediment-water interface. These results suggest that seafloor habitat heterogeneity contributes to the distribution of benthic foraminifera, including in low-oxygen environments. We submit that paleo-oxygenation methods that use epifaunal indicator taxa need to reconsider the dissolved oxygen requirements of epifaunal taxa

Temporal variability in living deep-sea benthic Foraminifera: a review: Earth-Science Review, v

Abstract The deep ocean environment is disturbed by various processes, many of which involve episodic inputs of organic matter. Ž . Some inputs e.g., phytodetritus at mid-high latitudes in the North Atlantic and Northeast Pacific are seasonally pulsed, Ž . others e.g., falls of whale carcasses are irregular and unpredictable, but together, they evoke a variety of responses from the benthic biota. In the case of deep-sea foraminifera, only those responses arising from seasonal food pulses have been fairly Ž . well-documented. The population dynamics of deep-sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely-related parameters, the flux of organic matter to the seafloor and Ž . concentrations of oxygen in the sediment porewater. Organic matter food inputs are most intense along bathyal continental margins, and their oxidation often leads to the depletion of oxygen in surface sediments. Under these conditions, foraminiferal faunas are dominated by low-oxygen tolerant, infaunal species, the abundance of which fluctuate in response to Ž . seasonally varying amounts of food and oxygen. At some sites e.g., Sagami Bay, off Japan , species migrate up and down Ž in the sediments, tracking critical oxygen concentrations. Where oxygen concentrations are consistently low less than about y1 . 0.5 ml l , as in parts of the California Borderland, foraminifera may undergo population increases solely in response to food pulses. In the abyssal North Atlantic, and in some continental margin areas of this ocean, organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments. These systems are food limited and seasonal Ž . population fluctuations reflect the availability of food phytodetritus rather than oxygen. Here, the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse Ž 2 . communities 2 or 3 out of ) 120 species per core of 25.5 cm surface area . Seasonal phytodetrital pulses to the deep-seafloor, and hence, foraminiferal population dynamics, are not entirely predictable. Being dependent on climatic and Ž Ž . upper-ocean processes, they vary in intensity from year to year and occasionally e.g., at the Porcupine Abyssal Plain PAP . Ž . in 1997 fail to materialise. Foraminiferal responses to irregular non-seasonal organic matter inputs are poorly-known. However, there is some evidence that whale falls, turbidite deposits, hydrothermal vents and seeps are exploited by species typical of organically-enriched, low-oxygen environments rather than by a specialised fauna. Fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer-term changes in palaeoproductivity. However, the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations ) Ž . Ž . Corresponding author. Tel.: q44-0 1703-596353; Fax: q44-0 1703-596247; E-mail: [email protected]. 1 E-mail: [email protected] 0012-8252r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 1 2 -8 2 5 2 9 9 0 0 0 1 0 -0 ( ) A.J. Gooday, A.E. Rathburnr Earth-Science ReÕiews 46 1999 187-212 188 between benthic foraminiferal ecology and seasonal phenomena in the deep ocean. q 1999 Elsevier Science B.V. All rights reserved

A New Biological Proxy for Deep-Sea Paleo-Oxygen: Pores of Epifaunal Benthic Foraminifera

The negative consequences of fossil fuel burning for the oceans will likely include warming, acidification and deoxygenation, yet predicting future deoxygenation is difficult. Sensitive proxies for oxygen concentrations in ancient deep-ocean bottom-waters are needed to learn from patterns of marine deoxygenation during global warming conditions in the geological past. Understanding of past oxygenation effects related to climate change will better inform us about future patterns of deoxygenation. Here we describe a new, quantitative biological proxy for determining ocean paleo-oxygen concentrations: the surface area of pores (used for gas exchange) in the tests of deep-sea benthic foraminifera collected alive from 22 locations (water depths: 400 to 4100 m) at oxygen levels ranging from ~ 2 to ~ 277 μmol/l. This new proxy is based on species that are widely distributed geographically, bathymetrically and chronologically, and therefore should have broad applications. Our calibration demonstrates a strong, negative logarithmic correlation between bottom-water oxygen concentrations and pore surface area, indicating that pore surface area of fossil epifaunal benthic foraminifera can be used to reconstruct past changes in deep ocean oxygen and redox levels

Epifaunal Foraminifera in an Infaunal World: Insights Into the Influence of Heterogeneity on the Benthic Ecology of Oxygen-Poor, Deep-Sea Habitats

A reduction in dissolved oxygen availability in marine habitats is among the predicted consequences of increasing global temperatures. An understanding of past oxygenation is critical for predictions of future changes in the extent and distribution of oxygen minimum zones (OMZs). Benthic foraminifera have been used to assess changes in paleo-oxygenation, and according to prevailing thought, oxygen-poor marine benthic habitats are dominated by sediment-dwelling infaunal foraminifera, while more oxygenated environments are populated with more epifaunal taxa. However, in this study we found elevated densities of epifaunal taxa in oxygen-poor habitats. A series of 16 multicores were taken on depth transects (360–3000 m) across an OMZ in the Southern California Bight to investigate the ecology of living (rose bengal stained) benthic foraminifera. Dissolved oxygen concentrations in bottom water at sampling sites varied from 21 to 162 μmol/l. Sampling focused on bathymetric highs in an effort to collect seafloor surface materials with coarse sediments in areas not typically targeted for sampling. Mean grain size varied from about 131 (gravelly sand) to about 830 μm (coarse sand with fine gravel). Vertical distribution patterns (0–2 cm) were consistent with those of conspecifics reported elsewhere, and reconfirm that Cibicidoides wuellerstorfi and Hanzawaia nipponica have a living preference at or near the sediment-water interface. As expected, assemblages were dominated by infaunal taxa, such as Uvigerina and Bolivina, traditionally associated with the supersaturated, unconsolidated mud, characteristic of OMZ habitats, suggesting that these taxa are not sensitive to substrate type. However, despite dysoxic conditions (21–28 μmol/l), epifaunal taxa comprised as much as 36% of the stained population at the five sites with the coarsest mean grain size, while other measured environmental parameters remained relatively constant. We suggest that these epifaunal taxa, including C. wuellerstorfi, prefer habitats with coarse grains that allow them to remain at or above the sediment-water interface. These results suggest that seafloor habitat heterogeneity contributes to the distribution of benthic foraminifera, including in low-oxygen environments. We submit that paleo-oxygenation methods that use epifaunal indicator taxa need to reconsider the dissolved oxygen requirements of epifaunal taxa

Peruvian Margin living benthic foraminiferal distributions in percentage

This dataset concerns information on the living (rose Bengal stained) benthic foraminifera that was compiled from four independent datasets. They comprise 53 samples from the Peruvian continental margin from water depths of 48 to 2092 m between 1°45'S and 17°28'S that were collected during independent expeditions; in 1998 during Panorama Expedition, Leg 3a, with R/V Melville, in 2008 during R/V Meteor expeditions M77 Leg 1 & 2, in 2009, 2010 and 2011 onboard R/V SNP 2 and José Olaya Balandra and in 2017 during R/V Meteor expedition M137. The surface sediment samples in all studies comprise the topmost 10 or 30 mm. Dataset also presents in situ measurements of bottom water oxygen content and calculated values of Particulate organic carbon rain rates

I/Ca in epifaunal benthic foraminifera: A semi-quantitative proxy for bottom water oxygen in a multi-proxy compilation for glacial ocean deoxygenation

The decline in dissolved oxygen in global oceans (ocean deoxygenation) is a potential consequence of global warming which may have important impacts on ocean biogeochemistry and marine ecosystems. Current climate models do not agree on the trajectory of future deoxygenation on different timescales, in part due to uncertainties in the complex, linked effects of changes in ocean circulation, productivity and organic matter respiration. More (semi-)quantitative reconstructions of oceanic oxygen levels over the Pleistocene glacial cycles may provide a critical test of our mechanistic understanding of the response of oceanic oxygenation to climate change. Even the most promising proxies for bottom water oxygen (BWO) have limitations, which calls for new proxy development and a multi-proxy compilation to evaluate glacial ocean oxygenation. We use Holocene benthic foraminifera to explore I/Ca in Cibicidoides spp. as a BWO proxy. We propose that low I/Ca (e.g., 15%) may provide semi-quantitative estimates of low BWO in past oceans (e.g., <∼50 μmol/kg). We present I/Ca records in five cores and a global compilation of multiproxy data, indicating that bottom waters were generally less-oxygenated during glacial periods, with low O2 waters (<∼50 μmol/kg) occupying some parts of the Atlantic and Pacific Oceans. Water mass ventilation and circulation may have been important in deoxygenation of the glacial deep Pacific and South Atlantic, whereas enhanced remineralization of organic matter may have had a greater impact on reducing the oxygen content of the interior Atlantic Ocean