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1. Insights into the deglacial variability of phytoplankton community structure in the eastern equatorial Pacific Ocean using [231Pa/230Th]xs and opal-carbonate fluxes

   https://doi.org/10.1038/s41598-022-26593-1  

   Schimmenti, Danielle; Marcantonio, Franco; Hayes, Christopher T.; Hertzberg, Jennifer; Schmidt, Matthew; Sarao, John (December 2022, Scientific Reports)

   Abstract Fully and accurately reconstructing changes in oceanic productivity and carbon export and their controls is critical to determining the efficiency of the biological pump and its role in the global carbon cycle through time, particularly in modern CO₂source regions like the eastern equatorial Pacific (EEP). Here we present new high-resolution records of sedimentary²³⁰Th-normalized opal and nannofossil carbonate fluxes and [²³¹Pa/²³⁰Th]xs ratios from site MV1014-02-17JC in the Panama Basin. We find that, across the last deglaciation, phytoplankton community structure is driven by changing patterns of nutrient (nitrate, iron, and silica) availability which, in turn, are caused by variability in the position of the Intertropical Convergence Zone (ITCZ) and associated changes in biogeochemical cycling and circulation in the Southern Ocean. Our multi-proxy work suggests greater scrutiny is required in the interpretation of common geochemical proxies of productivity and carbon export in the EEP. 

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2. Dynamics of the Pacific Antarctic Circumpolar Current

   https://doi.org/10.14379/iodp.proc.383.2021  

   Lamy, F.; Winckler, G.; Alvarez Zarikian, C.A. (July 2021, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and is constricted to its narrowest extent in the Drake Passage. Fresh and cold Pacific surface and intermediate water flowing through the Drake Passage (cold-water route) and warm Indian Ocean water masses flowing through the Agulhas region (warm-water route) are critical for the South Atlantic contribution to Meridional Overturning Circulation changes. Furthermore, physical and biological processes associated with the ACC affect the strength of the ocean carbon pump and therefore are critical to feedbacks linking atmospheric CO2 concentrations, ocean circulation, and climate/cryosphere on a global scale. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, there are no deep-sea drilling paleoceanographic records from the Pacific sector of the ACC. To advance our understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 recovered sedimentary sequences at (1) three sites in the central South Pacific (CSP) (U1539, U1540, and U1541), (2) two sites at the Chilean margin (U1542 and U1544), and (3) one site from the pelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Because of persistently stormy conditions and the resulting bad weather avoidance, we were not successful in recovering the originally planned Proposed Site CSP-3A in the Polar Frontal Zone of the CSP. The drilled sediments at Sites U1541 and U1543 reach back to the late Miocene, and those at Site U1540 reach back to the early Pliocene. High sedimentation rate sequences reaching back to the early Pleistocene (Site U1539) and the late Pleistocene (Sites U1542 and U1544) were recovered in both the CSP and at the Chilean margin. Taken together, the sites represent a depth transect from ~1100 m at Chilean margin Site U1542 to ~4070 m at CSP Site U1539 and allow investigation of changes in the vertical structure of the ACC, a key issue for understanding the role of the Southern Ocean in the global carbon cycle. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic-, carbonate-, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep-ocean variations and their relation to atmosphere and cryosphere changes. 

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3. Expedition 383 Scientific Prospectus: Dynamics of the Pacific Antarctic Circumpolar Current (DYNAPACC)

   https://doi.org/10.14379/iodp.sp.383add.2018  

   Lamy, F.; Winckler, G.; Alvarez Zarikian, C.A. (August 2018, Scientific prospectus)

   null (Ed.)

   The Antarctic Circumpolar Current (ACC) is the world’s strongest zonal current system that connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and constricted to its narrowest extent in the Drake Passage. Transport of fresh and cold surface and intermediate water masses through the Drake Passage (cold-water route) strongly affect the Atlantic Meridional Overturning Circulation (AMOC) together with the inflow of Indian Ocean water masses (warm-water route). Both oceanographic corridors are critical for the South Atlantic contribution to AMOC changes. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, deep-sea drilling records of the Pacific sector of the ACC lack information on its Cenozoic paleoceanography. To advance our knowledge and understanding of Plio-Pleistocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 proposes the recovery of 180 to 500 m long high-resolution Plio-Pleistocene sediment sequences at (1) three primary sites located on a cross-frontal transect in the central South Pacific (CSP) between the modern Polar Front (Site CSP-3A) and the Subantarctic Zone (Sites CSP-1A and CSP-2B), (2) two sites (CHI-1C and CHI-4B) at the Chilean margin, and (3) one site from the pelagic eastern South Pacific (ESP; Site ESP-1A) close to the entrance to the Drake Passage. The planned sites represent a depth transect from ~1100 m at the Chilean margin (Site CHI-4B) to >5000 m in the Bellingshausen Sea (Site CSP-3A) that will allow investigation of Plio-Pleistocene changes in the vertical structure of the ACC—a key issue for understanding the role of the Southern Ocean in the global carbon cycle. All of the six primary and eight alternate sites were surveyed with seismic lines in 2009–2010 and most recently in 2016. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic, carbonate, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep ocean variations and their relation to atmosphere and cryosphere changes through stadial-to-interstadial, glacial-to-interglacial, and warmer-than-present time intervals. 

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4. Expedition 383 Scientific Prospectus: Dynamics of the Pacific Antarctic Circumpolar Current (DYNAPACC)

   https://doi.org/10.14379/iodp.sp.383.2018  

   Lamy, F; Winckler, G; Alvarez_Zarikian, CA (August 2018, International Ocean Discovery Program)

   The Antarctic Circumpolar Current (ACC) is the world’s strongest zonal current system that connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and constricted to its narrowest extent in the Drake Passage. Transport of fresh and cold surface and intermediate water masses through the Drake Passage (cold-water route) strongly affect the Atlantic Meridional Overturning Circulation (AMOC) together with the inflow of Indian Ocean water masses (warm-water route). Both oceanographic corridors are critical for the South Atlantic contribution to AMOC changes. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, deep-sea drilling records of the Pacific sector of the ACC lack information on its Cenozoic paleoceanography. To advance our knowledge and understanding of Plio-Pleistocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 proposes the recovery of 180 to 500 m long high-resolution Plio-Pleistocene sediment sequences at (1) three primary sites located on a cross-frontal transect in the central South Pacific (CSP) between the modern Polar Front (Site CSP-3A) and the Subantarctic Zone (Sites CSP-1A and CSP-2B), (2) two sites (CHI-1C and CHI-4B) at the Chilean margin, and (3) one site from the pelagic eastern South Pacific (ESP; Site ESP-1A) close to the entrance to the Drake Passage. The planned sites represent a depth transect from ~1100 m at the Chilean margin (Site CHI-4B) to >5000 m in the Bellingshausen Sea (Site CSP-3A) that will allow investigation of Plio-Pleistocene changes in the vertical structure of the ACC—a key issue for understanding the role of the Southern Ocean in the global carbon cycle. All of the six primary and eight alternate sites were surveyed with seismic lines in 2009–2010 and most recently in 2016. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic, carbonate, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep ocean variations and their relation to atmosphere and cryosphere changes through stadial-to-interstadial, glacial-to-interglacial, and warmer-than-present time intervals. 

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5. Comparison of Late Neogene U ^k′ ₃₇ and TEX ₈₆ Paleotemperature Records From the Eastern Equatorial Pacific at Orbital Resolution

   https://doi.org/10.1029/2020PA003858  

   Lawrence, K. T.; Pearson, A.; Castañeda, I. S.; Ladlow, C.; Peterson, L. C.; Lawrence, C. E. (June 2020, Paleoceanography and Paleoclimatology)

   Abstract Key features of late Neogene climate remain uncertain due to conflicting records derived from different sea surface temperature (SST) proxies. To understand scenarios in which proxy‐derived temperature estimates can be used interchangeably or are instead measuring different aspects of the same system, it is necessary to explore both the consistencies and differences between specific paleothermometers. Here, we report orbital‐scale climate records from ODP Site 846 in the eastern equatorial Pacific (EEP) for the interval from ~5–6 Ma using alkenone and archaeal lipid paleothermometers. Results from both proxies are similar in their secular trends and magnitude of long‐term temperature change, and spectral analysis demonstrates that the records are coherent and in‐phase in both the obliquity and precession bands. However, we find that the temperatures reconstructed by TEX₈₆are consistently offset toward colder values by ~2 °C relative to U^k′₃₇‐derived temperatures in global calibrations, or by ~0.8 °C in Bayesian‐based calibrations. All combinations of calibrations also yield approximately twice the amplitude of orbital‐scale variation in TEX₈₆relative to U^k′₃₇‐derived temperature fluctuations. Both temperature proxies are negatively correlated with sedimentary alkenone concentrations, which we use as an indicator of increased export productivity. Removing this productivity contribution from TEX₈₆results in an adjusted TEX₈₆record with temperature sensitivity identical to U^k′₃₇. In future applications, this signal may be decoupled using additional sedimentary indicators of paleoproductivity, which likely will be most important for upwelling zone environments. There remain other nonexplained factors that contribute to differences between TEX₈₆and U^k′₃₇that warrant additional investigation. 

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