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A Closer Look At Benthic Foraminiferal Species

My fascination with teaching and research has been fostered by 15 years of graduate teaching and mentoring while I was a professor and a postdoc. My teaching career involved discussions, field sampling, and laboratory procedures to understand interactions between Benthic Foraminiferal species (Figure 1) and abiotic parameters in the interface sediment-water in a spatial and temporal scale using environmental indicators and multivariate analysis.

Figure 1: Benthic foraminiferal species. Image courtesy Patricia Eichler

I am a Biological Oceanographer interested in an array of disciplines including ecology, sedimentology, marine geology, biogeochemistry, sedimentology, geo biosciences, and paleoclimatology, but not limited to it. I am especially interested in the Foraminiferal species pattern which reflects sedimentological properties, climate change, modern mixing of marine and fresh waters in relation to pollution in mangroves, estuaries, coral reefs, continental shelves, and deep water both in the recent and in paleoenvironments.

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I like to explore whether benthic foraminiferal assemblages are sensitive to bottom water temperatures and nutrient levels in the western Pacific using sites recovered during IODP Leg 363. I study warm- versus cold- adapted species, establishing a warm water species curve (percent warm water species with respect to the total warm plus cold adapted forms). I also work trying to show that, on the spatial scale, the percent of warm water species from the youngest intervals (the core catchers of the first core) can be significantly correlated with modern bottom water temperatures. This supports that benthic foraminifera are temperature-sensitive, even to a small range of temperatures bracketed by the study sites (~2-5 degrees C). Down-core variations can be related to global climate background condition, although in a more general sense. My study supports the use of benthic foraminiferal assemblages as a tracer for bottom water temperatures and provides justification for follow-up higher resolution studies.

Also, methane releases from marine reservoirs are linked to climate change because of temperature changes during the Quaternary period. This assumption is based on variations in benthic foraminiferal stable isotope signatures due to the response of the methane flux on the faunal characteristics and geochemistry of the assemblages that I research. Cosmopolitan calcareous foraminiferal assemblages as Uvigerina, Bolivina, Chilostomella, Globobulimina, and Nonionella were some of the paleoceanographically important taxa associated with seeps in organic-rich environments from cold methane seeps.

Seep foraminifera are attracted to the availability of food at cold seeps and require no adaptations beyond those needed for life in organic-rich, reducing environments. It suggests that d13C values of foraminiferal tests reflect methane seepage and species-specific differences in isotopic composition and can indicate temporal variations in seep activity. Hydrothermal alteration and mobilization reinjects buried carbon into the hydrosphere and potentially atmosphere, a process believed to be linked to major shifts in global climate and mass-extinction events throughout earth history that can be tracked by foraminifera. Subsurface microbial populations can intercept and process these hydrothermally generated and mobilized carbon sources, hydrocarbons, and methane.

The great volume of magma associated with organic‚Äźrich sediments, thermal alterations, and associated carbon release are detected by the fauna living in the interface sediment-water. Therefore, a better understanding of foraminiferal ecology and stable isotopic composition will enhance paleo-seep recognition, and improve interpretations of climatic and paleoceanographic changes. I focus on foraminiferal population dynamics and their interactions trying to point out sediment alteration and accumulation and sill emplacement in the past.

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High-resolution continuous records, such as those from the marine realm, provide an outstanding opportunity to pair fossil occurrences with geochemical environmental proxies to examine the possible causes of mass extinctions. For example, the Mid Pleistocene transition (MPT, ‚ąľ1.2‚Äď0.6 Ma) was characterized by global cooling, glacial stage lengthening, changing ocean circulation, and evolution of terrestrial and marine biota. During the MPT, a stepwise extinction of over 100 species of deep-water benthic foraminifera occurred, targeted to a specific morphological group (largely the elongated “stilostomellids” with ornamented apertures, known as the “extinction group”). The Foraminiferal ecology and stable isotopic compositions of living (Rose Bengal stained) from top cores and of dead (fossil) foraminifera (>150mm) from cores off cold methane seeps in 1600 to 2000m of water depth. I generate a low-resolution record that captures variations in sediment to investigate potential applications for reconstructions of methane release in the past and present to increase our understanding of the conditions that limit life in the deep biosphere in these methane seeps.

These findings are described in the article entitled Foraminiferal zonation from a subtropical mangrove in Bertioga Channel (S√£o Paulo, SP, Brazil), recently published in the journal Regional Studies in Marine Science.

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