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1. Decreasing Foraminiferal Flux in Response to Ongoing Climate Change in Santa Barbara Basin, California.

   Havard, Emily E (June 2024, North Carolina State University Libraries)

   The geologically rapid response of foraminiferal assemblages to changing climate makes their shells an invaluable geological record of the past. However, just how rapid these changes are is unknown and the specific drivers of assemblage composition and abundance are complex. Understanding how modern foraminifera respond to and record a climate event that would appear nearly instantaneous in the sediment record can inform paleontological interpretations and help to place foraminifera in a broader ecological context. We focus on the impact of ongoing, rapid climate change on planktic foraminifera in the California Current ecosystem. The Santa Barbara Basin sediment trap, located off the coast of California, USA since 1993, provides a 28-year record of particulate and foraminiferal flux to the basin. The sediment trap captures the superposition of the annual cycle of seasonal upwelling in Santa Barbara Basin, Pacific multiannual ENSO-driven temperature changes, and anthropogenically forced climate change. We present data on planktic foraminiferal flux collected between 2014-2021, at two-week intervals (164 samples, 60,006 individuals) and compare results to previously published data from 1993-1998. Consistent with previous studies, the most abundant species in both periods were Globigerina bulloides, Neogloboquadrina incompta, and Turborotalita quinqueloba, with peak flux in the spring and summer. The winter season is characterized by low flux and an increase in abundance of N. incompta and subtropical species. We find a 37.9 % decrease in total foraminiferal flux relative to the 1990s primarily driven by a decrease in G. bulloides abundance and accompanied by a 21.9 % decrease in calcium carbonate flux. We also find a decrease in subtropical species flux and relative abundance (Globigerinoides ruber, Globoturborotalita rubescens, Orbulina universa, Neogloboquadrina dutertrei) compared to the 1990s, contrary to expectations if assemblages were to primarily follow a trend dominated by anthropogenic warming. We hypothesize that the observed decrease in flux is likely related to an increase in both upwelling and acidification of the California coastal upwelling system. This extremely rapid response of foraminifera to ongoing changes in carbonate chemistry and temperature is already having a meaningful impact on carbon cycling. 

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2. Response of Planktic Foraminifera to Rapid Climate Change in the California Current Ecosystem: Implications for Proxy Applications

   Havard, E; Cherry, K; Tappa, E; Benitez-Nelson, C; Davis, CV (December 2023, American Geophysical Union)

   The rapid response of foraminiferal assemblages to changing climate makes their shells an invaluable geological record of the past. The drivers of shell assemblage composition and abundance, however, are complex and involve both oceanographic and ecological processes. Understanding how modern foraminifera respond to and record a climate event that would appear nearly instantaneous in the sediment record can inform paleontological interpretations and help to place foraminifera in a broader ecological context. We focus on the impact of rapid climate change on planktic foraminifera in the California Current ecosystem, providing insight into how foraminiferal response to abrupt environmental change informs their use as paleoenvironmental proxies. The Santa Barbara Basin sediment trap, located off the coast of California, USA, provides a record of particulate and foraminiferal flux to the basin since 1993. The 30-year deployment of the sediment trap captures the superposition of the annual cycle of seasonal upwelling in Santa Barbara Basin, Pacific multiannual ENSO-driven temperature changes, and anthropogenically forced climate change. We present data on planktic foraminiferal flux collected between 2014-2021, at two-week intervals (> 150 samples) and compare results to previously published data from 1993-1998. Consistent with previous studies, the most abundant species between 2014-2021 are Globigerina bulloides, Neogloboquadrina incompta, and Turborotalita quinqueloba, with peak flux in the spring and late summer. The winter season is characterized by low flux and an increase in abundance of N. incompta and subtropical species. Seasonal and interannual variability affect the interpretation of foraminiferal records across geologic time. For example, G. bulloides exhibits strong seasonal trends within any single year, but has an inconsistent seasonality across multiple years, making G. bulloides a poor proxy for spring upwelling conditions in Santa Barbara. We find that the most modern samples (2018-2021) show a decrease in subtropical species abundance (Globigerinoides ruber, Globigerina rubescens, Orbulina universa, Neogloboquadrina dutertrei) compared to the 1990s, contrary to expectations if assemblages were to primarily follow a trend dominated by anthropogenic warming. 

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3. Seasonality in planktic foraminifera of the central California coastalupwelling region

   https://doi.org/10.5194/bg-13-5139-2016  

   Davis, Catherine V.; Hill, Tessa M.; Russell, Ann D.; Gaylord, Brian; Jahncke, Jaime (January 2016, Biogeosciences)

   Abstract. The close association between planktic foraminiferal assemblages and local hydrography make foraminifera invaluable proxies for environmental conditions. Modern foraminiferal seasonality is important for interpreting fossil distributions and shell geochemistry as paleoclimate proxies. Understanding this seasonality in an active upwelling area is also critical for anticipating which species may be vulnerable to future changes in upwelling intensity and ocean acidification. Two years (2012–2014) of plankton tows, along with conductivity–temperature–depth profiles and carbonate chemistry measurements taken along the north-central California shelf, offer new insights into the seasonal dynamics of planktic foraminifera in a seasonal coastal upwelling regime. This study finds an upwelling affinity for Neogloboquadrina pachyderma as well as a seasonal and upwelling associated alternation between dominance of N. pachyderma and Neogloboquadrina incompta, consistent with previous observations. Globigerina bulloides, however, shows a strong affinity for non-upwelled waters, in contrast to findings in Southern California where the species is often associated with upwelling. We also find an apparent lunar periodicity in the abundances of all species and document the presence of foraminifera even at very low saturation states of calcite. 

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4. Planktic Foraminiferal Response to the 2014-2015 Marine Heatwave in the Santa Barbara Basin

   Cherry, K; Havard, E; Benitez-Nelson, C; Tappa, E; Davis, CV (December 2023, American Geophysical Union)

   As the oceans warm the severity and frequency of marine heatwaves (MHW) is expected to escalate and have significant detrimental impacts on marine ecosystems. However, limited data exists to provide a pre-anthropogenic baseline for MHW or suggest whether their frequency may have changed in the geologic past. Planktic foraminifera, ubiquitous marine protozoa with a calcareous test, serve as a common paleoceanographic proxy due to their sensitivity to sea surface temperature, among other environmental parameters. Changes in foraminiferal assemblage compositions recovered from sediments may therefore be used as potential proxies for MHW, but the responses of planktic foraminifera to MHW remains understudied. This research explores the foraminiferal community off the California coast in the high sedimentation-rate Santa Barbara Basin (SBB) (34°14'N, 120°02'W) during 2014-2015. At this time, the Pacific Ocean experienced a MHW known as the 'Warm Blob,' that increased average water temperatures by 4°C. We present data from 30 planktic foraminiferal assemblages collected at 10-13-day intervals in a sediment trap moored between 400-500 m below the sea surface in the SBB. The most abundant species between 2014-2015 are Neogloboquadrina incompta, Globigerina bulloides, and Turborotalita quinqueloba. Other notable species are Globigerinoides ruber (pink), Orbulina universa, and Globorotalia scitula. To assess potential differences in assemblages from non-anomalous years, we compare these findings with data on assemblages from 1993-1996, 2017-2018, and 2020-2021. Data from the SBB will also be contrasted with plankton tow data collected along the Newport Hydrographic line between 2014-2016 to investigate the impact of MHW on zonal distribution1. Examining the predictability of foraminiferal assemblages during MHW will provide insights into their potential use as a proxy for MHW in the geologic past. 

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5. Morphotypical and Geochemical Variations of Planktic Foraminiferal Species in Siberian and Central Arctic Ocean Core Tops

   https://doi.org/10.61551/gsjfr.54.1.1  

   Prabhakar, Maya; Thirumalai, Kaustubh; Cronin, Thomas M; Gemery, Laura; Thomas, Elizabeth K; Rafter, Patrick A (January 2024, Journal of Foraminiferal Research)

   Abstract In this work, we utilize a transect of core top, mid- to late Holocene, sediments from the Eastern Siberian Sea to the central Arctic Ocean, spanning gradients in upper-ocean water column properties, to examine regional planktic foraminiferal species abundances and geochemistry. We present species- and morphotype-specific foraminiferal assemblages at these sites and stable isotope analyses of neogloboquadrinids. We find little variation in planktic species populations, and only small variations in N. pachyderma morphotype distributions, between sites. Spatial averages of N. pachyderma morphotype and N. incompta δ18O values show no significant differences, suggesting a similar calcification depth for all morphotypes of N. pachyderma and N. incompta across our sites, which we estimate to be between ∼ 50–150 m. Values of δ18O of a group of unencrusted specimens delineate a shallower calcification habitat. Neogloboquadrina pachyderma-2 Mg/Ca values yield temperatures outside the range of observations using available calibration equations, pointing toward the need for more Arctic-specific Mg/Ca-temperature calibrations. 

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