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1. Planktonic foraminiferal assemblages reflect warming during two recent mid-latitude marine heatwaves

   https://doi.org/10.3389/fmars.2023.1155761  

   Lane, M. Kelsey; Fehrenbacher, Jennifer S.; Fisher, Jennifer L.; Fewings, Melanie R.; Crump, Byron C.; Risien, Craig M.; Meyer, Grace M.; Schell, Faith (March 2023, Frontiers in Marine Science)

   Under future climate scenarios, ocean temperatures that are presently extreme and qualify as marine heatwaves (MHW) are forecasted to increase in frequency and intensity, but little is known about the impact of these events on one of the most common paleoproxies, planktonic foraminifera. Planktonic foraminifera are globally ubiquitous, shelled marine protists. Their abundances and geochemistry vary with ocean conditions and fossil specimens are commonly used to reconstruct ancient ocean conditions. Planktonic foraminiferal assemblages are known to vary globally with sea surface temperature, primary productivity, and other hydrographic conditions, but have not been studied in the context of mid-latitude MHWs. For this study, the community composition and abundance of planktonic foraminifera were quantified for 2010-2019 along the Newport Hydrographic Line, a long-term monitoring transect at 44.6°N in the Northern California Current (NCC). Samples were obtained from archived plankton tows spanning 46 to 370 km offshore during annual autumn (August – October) cruises. Two MHWs impacted the region during this timeframe: the first during 2014-2016 and a second, shorter duration MHW in 2019. During the 2014-2016 MHW, warm water subtropical and tropical foraminifera species were more prevalent than the typical polar, subpolar, and transitional species common to this region. Cold water species were abundant again after the first MHW dissipated in late 2016. During the second, shorter-duration MHW in 2019, the assemblage consisted of a warm water assemblage but did not include tropical species. The foraminiferal assemblage variability correlated with changes in temperature and salinity in the upper 100 meters and was not correlated with distance offshore or upwelling. These results suggest that fossil foraminiferal assemblages from deep sea sediment cores may provide insight into the magnitude and frequency of past MHWs. 

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2. 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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3. Unique Habitat for Benthic Foraminifera in Subtidal Blue Holes on Carbonate Platforms

   https://doi.org/10.3389/fevo.2021.794728  

   Little, Shawna N.; van Hengstum, Peter J.; Beddows, Patricia A.; Donnelly, Jeffrey P.; Winkler, Tyler S.; Albury, Nancy A. (December 2021, Frontiers in Ecology and Evolution)

   Dissolution of carbonate platforms, like The Bahamas, throughout Quaternary sea-level oscillations have created mature karst landscapes that can include sinkholes and off-shore blue holes. These karst features are flooded by saline oceanic waters and meteoric-influenced groundwaters, which creates unique groundwater environments and ecosystems. Little is known about the modern benthic meiofauna, like foraminifera, in these environments or how internal hydrographic characteristics of salinity, dissolved oxygen, or pH may influence benthic habitat viability. Here we compare the total benthic foraminiferal distributions in sediment-water interface samples collected from <2 m water depth on the carbonate tidal flats, and the two subtidal blue holes Freshwater River Blue Hole and Meredith’s Blue Hole, on the leeward margin of Great Abaco Island, The Bahamas. All samples are dominated by miliolid foraminifera (i.e.,QuinqueloculinaandTriloculina), yet notable differences emerge in the secondary taxa between these two environments that allows identification of two assemblages: a Carbonate Tidal Flats Assemblage (CTFA) vs. a Blue Hole Assemblage (BHA). The CTFA includes abundant common shallow-water lagoon foraminifera (e.g.,Peneroplis,Rosalina,Rotorbis), while the BHA has higher proportions of foraminifera that are known to tolerate stressful environmental conditions of brackish and dysoxic waters elsewhere (e.g.,Pseudoeponides,Cribroelphidium,Ammonia). We also observe how the hydrographic differences between subtidal blue holes can promote different benthic habitats for foraminifera, and this is observed through differences in both agglutinated and hyaline fauna. The unique hydrographic conditions in subtidal blue holes make them great laboratories for assessing the response of benthic foraminiferal communities to extreme environmental conditions (e.g., low pH, dysoxia). 

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4. 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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5. Ecological and Environmental Stability in Offshore Southern California Marine Basins Through the Holocene

   https://doi.org/10.1029/2021PA004373  

   Palmer, Hannah M.; Hill, Tessa M.; Kennedy, Esther G.; Roopnarine, Peter D.; Langlois, Sonali; Reyes, Katherine R.; Stott, Lowell D. (August 2022, Paleoceanography and Paleoclimatology)

   Abstract In the face of ongoing marine deoxygenation, understanding timescales and drivers of past oxygenation change is of critical importance. Marine sediment cores from tiered silled basins provide a natural laboratory to constrain timing and implications of oxygenation changes across multiple depths. Here, we reconstruct oxygenation and environmental change over time using benthic foraminiferal assemblages from sediment cores from three basins across the Southern California Borderlands: Tanner Basin (EW9504‐09PC, 1,194 m water depth), San Nicolas Basin (EW9504‐08PC, 1,442 m), and San Clemente Basin (EW9504‐05PC,1,818 m). We utilize indicator taxa, community ecology, and an oxygenation transfer function to reconstruct past oxygenation, and we directly compare reconstructed dissolved oxygen to modern measured dissolved oxygen. We generate new, higher resolution carbon and oxygen isotope records from planktic (Globigerina bulloides) and benthic foraminifera (Cibicides mckannai) from Tanner Basin. Geochemical and assemblage data indicate limited ecological and environmental change through time in each basin across the intervals studied. Early to mid‐Holocene (11.0–4.7 ka) oxygenation below 1,400 m (San Clemente and San Nicolas) was relatively stable and reduced relative to modern. San Nicolas Basin experienced a multi‐centennial oxygenation episode from 4.7 to 4.3 ka and oxygenation increased in Tanner Basin gradually from 1.7 to 0.8 ka. Yet across all three depths and time intervals studied, dissolved oxygen is consistently within a range of intermediate hypoxia (0.5–1.5 ml L⁻¹[O₂]). Variance in reconstructed dissolved oxygen was similar to decadal variance in modern dissolved oxygen and reduced relative to Holocene‐scale changes in shallower basins. 

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