Foraminifera are immensely successful and diverse components of deep-sea benthic communities, encompassing an extraordinary range of morphotypes and ecological traits. Bathymetric and geographic distributions are strongly influenced by organic-matter fluxes and carbonate dissolution. Species occupying different microhabitats within the sediment exhibit different ecological characteristics. Shallow-infaunal species are often active in processing labile organic matter and show seasonal population fluctuations; deeper infaunal species are less responsive and have more stable populations. Some foraminifera are highly tolerant of hypoxia, exhibiting ultrastructural and physiological adaptations to these stressful conditions, including the ability to respire nitrate. The structure and composition of fossil foraminiferal assemblages, and geochemical signals preserved in their calcareous shells, provide important proxies for reconstructing ancient oceans, particularly during the Late Cenozoic.

Deep-Sea Benthic Foraminifera

Protist diversity and function in the dark ocean - Challenging the paradigms of deep-sea ecology with special emphasis on foraminiferans and naked protists.

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

. 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 the dependant variable. The correlation was
significant ( R2=0.82 ; p ), 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 three sediment cores from the northern
part of the Peruvian OMZ between 3 and 8 ∘  S and 997
and 1250 m water depth, 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 LGM and the Holocene was constrained to 30  µ mol kg −1 at the lower boundary of the OMZ.

/pdf/bottom-water-deoxygenation-at-the-peruvian-margin-during-the-3btfsmfacx.pdf

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

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 sixteen 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 mol/l to 162 mol/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 131m (gravelly sand) to about 830μm (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 mol/l to 28 mol/l ), epifaunal taxa comprised as much as 36 percent 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.

/pdf/epifaunal-foraminifera-in-an-infaunal-world-insights-into-3c5kp9oxva.pdf

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

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.

/pdf/a-new-biological-proxy-for-deep-sea-paleo-oxygen-pores-of-4jnvktx0p3.pdf

Jake Willingham

Papers

A New biological proxy for deep-sea paleo-oxygen: Pores of epifaunal benthic foraminifera.

The distribution of deep-sea benthic foraminifera living along the southern margin of australia