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1. Spatiotemporal variability of benthic and planktonic foraminifera off the coast of San Diego

   Renssen, B.; Gray, S.C. (November 2021, CERF 26th Biennial Conference)

   no editor (Ed.)

   Foraminifera (single celled protists with tests primarily of Calcium Carbonate) are directly influenced by ocean warming and hydrographic changes such as expansion of the low oxygen areas associated with anthropogenic climate change. Benthic and planktonic foraminifera communities are good indicators of hydrographic conditions at the sea-floor and sea surface, respectively. Though previous studies have demonstrated that there has been overall ocean surface warming in Southern California and that the oxygen minimum zone has expanded, the relationship between water temperature, dissolved oxygen and foraminifera abundance in the area offshore San Diego has not been extensively examined. Cored sediment samples along with hydrographic data collected during annual research cruises (2001-2012, 2018) on the RV Sproul at three stations (water depth 100 m, 200m 300 m) due west from San Diego, CA provide an opportunity to evaluate how benthic and planktonic foraminiferal communities have changed over the past 19 years. The objective of this research was to identify the foraminifera in these sediments and compare patterns between years to temperature and dissolved oxygen (DO). Sediment samples from the upper 1 cm of the seafloor using a multicore were sieved and the foraminifera were picked and examined under a Leica S9i microscope for identification to genus. Sea surface and bottom water temperature and DO concentrations were measured using a CTD. Analyses of the variation between sites and over time will indicate whether benthic and planktonic community changes track environmental changes in temperature and dissolved oxygen, providing valuable data to assess whether climate change is impacting marine communities. 

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2. Environmental correlates of molluscan predator–prey body size in the northern Gulf of Mexico

   https://doi.org/10.1017/pab.2023.22  

   Calderaro, Luke A.; Harnik, Paul G.; Rillo, Marina C. (February 2024, Paleobiology)

   The Mississippi River watershed drains 40% of the continental United States, and the tremendous primary productivity in the adjacent north-central Gulf of Mexico has created one of the most extensive dead zones on Earth. In contrast, smaller watersheds deliver fewer nutrients to the northeastern gulf, and consequently, productivity is limited and hypoxia is uncommon. How has variation in primary productivity, oxygen availability, and sea-surface temperature affected coastal food webs? Here, we investigate environmental controls on the size of molluscan predators and prey in the northern Gulf of Mexico using Holocene death assemblages. Linear mixed models indicate that bivalve size and the frequency of drilling predation are affected by dissolved oxygen concentrations; drilling frequency declines with declining oxygen, whereas bivalve size increases. In contrast, sea-surface temperature is positively associated with the size of molluscan predators and prey. Net primary productivity contributes relatively little to predator or prey size, and predator-to-prey size ratios do not vary consistently with environmental conditions across the northern gulf. Larger bivalves in areas of oxygen limitation may be due to decreased predation pressure and, consequently, greater prey longevity. The larger size of bivalves and predatory gastropods in warmer waters may reflect enhanced growth under these conditions, provided dissolved oxygen concentrations exceed a minimum threshold. Holocene death assemblages can be used to test long-standing hypotheses regarding environmental controls on predator−prey body-size distributions through geologic time and provide baselines for assessing the ongoing effects of anthropogenic eutrophication and warming on coastal food webs. 

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3. The latitudinal temperature gradient and its climate dependence as inferred from foraminiferal δ ¹⁸ O over the past 95 million years

   https://doi.org/10.1073/pnas.2111332119  

   Gaskell, Daniel E.; Huber, Matthew; O’Brien, Charlotte L.; Inglis, Gordon N.; Acosta, R. Paul; Poulsen, Christopher J.; Hull, Pincelli M. (March 2022, Proceedings of the National Academy of Sciences)

   The latitudinal temperature gradient is a fundamental state parameter of the climate system tied to the dynamics of heat transport and radiative transfer. Thus, it is a primary target for temperature proxy reconstructions and global climate models. However, reconstructing the latitudinal temperature gradient in past climates remains challenging due to the scarcity of appropriate proxy records and large proxy–model disagreements. Here, we develop methods leveraging an extensive compilation of planktonic foraminifera δ 18 O to reconstruct a continuous record of the latitudinal sea-surface temperature (SST) gradient over the last 95 million years (My). We find that latitudinal SST gradients ranged from 26.5 to 15.3 °C over a mean global SST range of 15.3 to 32.5 °C, with the highest gradients during the coldest intervals of time. From this relationship, we calculate a polar amplification factor (PAF; the ratio of change in >60° S SST to change in global mean SST) of 1.44 ± 0.15. Our results are closer to model predictions than previous proxy-based estimates, primarily because δ 18 O-based high-latitude SST estimates more closely track benthic temperatures, yielding higher gradients. The consistent covariance of δ 18 O values in low- and high-latitude planktonic foraminifera and in benthic foraminifera, across numerous climate states, suggests a fundamental constraint on multiple aspects of the climate system, linking deep-sea temperatures, the latitudinal SST gradient, and global mean SSTs across large changes in atmospheric CO 2 , continental configuration, oceanic gateways, and the extent of continental ice sheets. This implies an important underlying, internally driven predictability of the climate system in vastly different background states. 

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4. ABUNDANCES, DIVERSITY, AND ECOLOGY OF BENTHIC FORAMINIFERA FROM THE SOUTHERN CALIFORNIA BIGHT

   Ononame, O.; Burkett, A.; Rathburn, A. (March 2023, Geological Society of America South Central Section)

   none. (Ed.)

   Foraminifera are single celled organisms that have tests that are composed of calcium carbonate or detrital materials. The assemblages of foraminifera have been influenced by their immediate environment which depict the influence and results of man’s activities and other natural processes that occur in the environment. These environmental changes include salinity, pH, hydrocarbon pollution and organic matter. With these factors, paleoenvironmental interpretations are made by identifying the different patterns in the foraminifera communities. Variations in oxygen concentrations at the sediment-water interface have a significant impact on benthic foraminiferal assemblages and morphologic properties. This is seen in the vertical distribution of foraminifera in response to factors such as food, pore water, and oxygen. This study documents foraminiferal ecology and abundances across an oxygen transect off the coast of San Diego. Available oxygen ranges from >1.0ml/l are considered oxic; O2 values from 0.1 - 1.0ml/l will be considered dysoxic and O2 values <0.10ml/l will be considered anoxic. Previous work in this region has suggested that sediment grain size, rather than oxygen availability, may have as much of an impact on foraminiferal assemblages. These observations were made based on the fact that Cibicidoides wuellerstorfi, an epibenthic foraminifera preferring elevated substrates in well-oxygenated environments, were found in greater abundances at areas with coarser grained materials despite low available oxygen. C. wuellerstorfi has also been found to have I/Ca and test porosity (size and abundance of pores on the surface of the test) which correlate to the available oxygen in bottom waters at the time of test formation. Not only will this study document foraminiferal assemblages and abundances across an oxygen transect, but C. wuellerstorfi from key oxygen environments will be examined under SEM and used in porosity and I/Ca analyses which will contribute to the development of a quantitative oxygen proxy. The development of this quantitative oxygen proxy is essential because despite oxygen being one of the primary variables influencing major geochemical and faunal responses within the world’s ocean, no clear proxy currently exists in paleoceanographic reconstructions. 

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5. BENTHIC FORAMINIFERA ASSEMBLAGES OFFSHORE OF SAN DIEGO AND THEIR VARIANCE WITH DISSOLVED OXYGEN AND DEPTH

   Meara, A.N.; Gray, S.C. (February 2022, Ocean Sciences Meeting)

   no editor (Ed.)

   The concentration of dissolved oxygen (DO) has decreased by about 2% over the past 50 years due to rising global temperatures and models predict further declines this century. However, little research has been done to examine how benthic foraminifera communities vary across a DO gradient offshore of southern California. The southern California continental margin is characterized by variable bathymetry and isolated low oxygen basins and high productivity and is an ideal location to investigate the impacts of DO and changing climate on benthic foraminifera. The objectives of this research were to 1) characterize how foraminifera communities vary spatially and with depth and DO and 2) to examine if there have been changes in these communities over the past 20 years. In 2018-19, sediment samples from the sedimentwater interface were collected using a multicorer at five sites of variable depth (200-900 m) from 10 to 170 kilometers offshore of southern California. Two of these sites had been sampled annually from 2001- 2012. Though the communities at all sites included most taxa, the relative percent and abundance of each taxa varied between sites. Sites with reduced DO were dominated by Uvigerina and Bolivina, with a large decrease in Cassidulina. Generally, the same morphotypes were seen across two decades of observation at two sites without a clear pattern of secular variability. Further studies should be done to examine how hypoxic-associated species vary across the full depth range of the oxygen minimum layer and whether these taxa are developing morphological adaptations to cope with the changing environment. 

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