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1. South Pacific Paleogene Climate

   https://doi.org/10.14379/iodp.proc.378.2022  

   Röhl, U.; Thomas, D.J.; Childress, L.B (February 2022, Proceedings of the International Ocean Discovery Program)

   International Ocean Discovery Program (IODP) Expedition 378 was designed to recover the first comprehensive set of Paleogene sedimentary sections from a transect of sites strategically positioned in the South Pacific Ocean to reconstruct key changes in oceanic and atmospheric circulation. These sites would have provided an unparalleled opportunity to add crucial new data and geographic coverage to existing reconstructions of Paleogene climate. Following the ~15 month postponement of Expedition 378 and subsequent port changes that resulted in a reduction of the number of primary sites, testing and evaluation of the research vessel JOIDES Resolution derrick in the weeks preceding the expedition determined that it would not support deployment of drill strings in excess of 2 km. Consequently, only one of the originally approved seven primary sites was drilled. Expedition 378 recovered the first continuously cored, multiple-hole Paleogene sedimentary section from the southern Campbell Plateau at Site U1553. This high–southern latitude site builds on the legacy of Deep Sea Drilling Project Site 277 (a single, partially spot cored hole), providing a unique opportunity to refine and expand existing reconstructions of Cenozoic climate history. As the world’s largest ocean, the Pacific Ocean is intricately linked to major changes in the global climate system. Previous drilling in the low-latitude Pacific Ocean during Ocean Drilling Program Legs 138 and 199 and Integrated Ocean Drilling Program Expeditions 320 and 321 provided new insights into climate and carbon system dynamics, productivity changes across the zone of divergence, time-dependent calcium carbonate dissolution, bio- and magnetostratigraphy, the location of the Intertropical Convergence Zone, and evolutionary patterns for times of climatic change and upheaval. Expedition 378 in the South Pacific Ocean uniquely complements this work with a high-latitude perspective, especially because appropriate high-latitude records are unobtainable in the Northern Hemisphere of the Pacific Ocean. Expedition 378 provides material from the South Pacific Ocean in an area critical for high-latitude climate reconstructions spanning the early Paleocene to late Oligocene. Site U1553 and the entire corpus of shore-based investigations will significantly contribute to the challenges of the “Climate and Ocean Change: Reading the Past, Informing the Future” theme of the 2013–2023 IODP Science Plan (How does Earth’s climate system respond to elevated levels of atmospheric CO2? How resilient is the ocean to chemical perturbations?). Furthermore, Expedition 378 provides material from the South Pacific Ocean in an area critical for high-latitude climate reconstructions spanning the Paleocene to late Oligocene. 

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2. Microbial community structure in the western tropical South Pacific

   https://doi.org/10.5194/bg-15-3909-2018  

   Bock, Nicholas; Van Wambeke, France; Dion, Moïra; Duhamel, Solange (January 2018, Biogeosciences)

   Abstract. Oligotrophic regions play a central role in global biogeochemical cycles, with microbial communities in these areas representing an important term in global carbon budgets. While the general structure of microbial communities has been well documented in the global ocean, some remote regions such as the western tropical South Pacific (WTSP) remain fundamentally unexplored. Moreover, the biotic and abiotic factors constraining microbial abundances and distribution remain not well resolved. In this study, we quantified the spatial (vertical and horizontal) distribution of major microbial plankton groups along a transect through the WTSP during the austral summer of 2015, capturing important autotrophic and heterotrophic assemblages including cytometrically determined abundances of non-pigmented protists (also called flagellates). Using environmental parameters (e.g., nutrients and light availability) as well as statistical analyses, we estimated the role of bottom–up and top–down controls in constraining the structure of the WTSP microbial communities in biogeochemically distinct regions. At the most general level, we found a typical tropical structure, characterized by a shallow mixed layer, a clear deep chlorophyll maximum at all sampling sites, and a deep nitracline. Prochlorococcus was especially abundant along the transect, accounting for 68±10.6% of depth-integrated phytoplankton biomass. Despite their relatively low abundances, picophytoeukaryotes (PPE) accounted for up to 26±11.6% of depth-integrated phytoplankton biomass, while Synechococcus accounted for only 6±6.9%. Our results show that the microbial community structure of the WTSP is typical of highly stratified regions, and underline the significant contribution to total biomass by PPE populations. Strong relationships between N₂ fixation rates and plankton abundances demonstrate the central role of N₂ fixation in regulating ecosystem processes in the WTSP, while comparative analyses of abundance data suggest microbial community structure to be increasingly regulated by bottom–up processes under nutrient limitation, possibly in response to shifts in abundances of high nucleic acid bacteria (HNA). 

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3. Transport of anthropogenic dissolved Pb in the South Pacific Ocean

   Lanning, N; Kim, Y; Dick, K; Fitzsimmons, J; Marcantonio, F; Boyle, E (December 2024, AGU)
4. Ecosystems services research in action: reflexively valuing environments in the South Pacific

   https://doi.org/10.5751/ES-12253-260224  

   Hunter, Chelsea E.; Lauer, Matthew (January 2021, Ecology and Society)
5. Anomalously high abundance of Crocosphaera in the South Pacific Gyre

   https://doi.org/10.1093/femsle/fnac039  

   Benavides, Mar; Caffin, Mathieu; Duhamel, Solange; Foster, Rachel Ann; Grosso, Olivier; Guieu, Cécile; Van Wambeke, France; Bonnet, Sophie (April 2022, FEMS Microbiology Letters)

   Abstract The unicellular diazotrophic cyanobacterium Crocosphaera contributes significantly to fixed nitrogen inputs in the oligotrophic ocean. In the western tropical South Pacific Ocean (WTSP), these diazotrophs abound thanks to the phosphorus-rich waters provided by the South Equatorial Current, and iron provided aeolian and subsurface volcanic activity. East of the WTSP, the South Pacific Gyre (SPG) harbors the most oligotrophic and transparent waters of the world's oceans, where only heterotrophic diazotrophs have been reported before. Here, in the SPG, we detected unexpected accumulation of Crocosphaera at 50 m with peak abundances of 5.26 × 105 nifH gene copies l–1. The abundance of Crocosphaera at 50 m was in the same order of magnitude as those detected westwards in the WTSP and represented 100% of volumetric N2 fixation rates. This accumulation at 50 m was likely due to a deeper penetration of UV light in the clear waters of the SPG being detrimental for Crocosphaera growth and N2 fixation activity. Nutrient and trace metal addition experiments did not induce any significant changes in N2 fixation or Crocosphaera abundance, indicating that this population was not limited by the resources tested and could develop in high numbers despite the oligotrophic conditions. Our findings indicate that the distribution of Crocosphaera can extend into subtropical gyres and further understanding of their controlling factors is needed. 

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