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1. Searles Lake evaporite sequences: Indicators of late Pleistocene/Holocene lake temperatures, brine evolution, and p CO2

   https://doi.org/10.1130/B35857.1  

   Olson, Kristian J. ; Lowenstein, Tim K. ( March 2021 , GSA Bulletin)

   Searles Lake, California, was a saline-alkaline lake that deposited >25 non-clastic minerals that record the history of lake chemistry and regional climate. Here, the mineralogy and petrography from the late Pleistocene/Holocene (32−6 ka) portion of a new Searles Lake sediment core, SLAPP-SRLS17, is combined with thermodynamic models to determine the geochemical and paleoclimate conditions required to produce the observed mineral phases, sequences, and abundances. The models reveal that the primary precipitates formed by open system (i.e., fractional crystallization), whereas the early diagenetic salts formed by salinity-driven closed system back-reactions (i.e., equilibrium crystallization). For core SLAPP-SRLS17, the defining evaporite sequence trona → burkeite → halite indicates brine temperatures within a 20−29 °C range, implying thermally insulating lake depths >10 m during salt deposition. Evaporite phases reflect lake water pCO2 consistent with contemporaneous atmospheric values of ∼190−270 ppmv. However, anomalous layers of nahcolite and thenardite indicate pulses of pCO2 > 700−800 ppm, likely due to variable CO2 injection along faults. Core sedimentology indicates that Searles Lake was continuously perennial between 32 ka and 6 ka such that evaporite units reflect periods of net evaporation but never complete desiccation. Model simulations indicate that cycles of partial evaporation and dilution strongly influence long-term brinemore »evolution by amassing certain species, particularly Cl−, that only occur in late-stage soluble salts. A model incorporating long-term brine dynamics corrects previous mass-balance anomalies and shows that the late Pleistocene/Holocene (32−6 ka) salts are partially inherited from the solutes introduced into earlier lakes going back at least 150 ka.« less
2. Late Holocene dust provenance at Siple Dome, Antarctica

   https://doi.org/10.1016/j.quascirev.2021.107271  

   Koffman, Bess G. ; Goldstein, Steven L. ; Winckler, Gisela ; Kaplan, Michael R. ; Kreutz, Karl J. ; Bolge, Louise ; Bory, Aloys ; Biscaye, Pierre ( December 2021 , Quaternary Science Reviews)
3. Hydroclimate Dipole drives multi‐centennial variability in the Western Tropical North Atlantic Margin During the Middle and Late Holocene.

   https://doi.org/10.1029/2020PA004184  

   Sullivan, Richard M. ; Hengstum, Peter J. ; Coats, Sloan J. ; Donnelly, Jeffrey P. ; Tamalavage, Anne E. ; Winkler, Tyler S. ; Albury, Nancy A. ( August 2021 , Paleoceanography and Paleoclimatology)

   Meridional shifts of the North Atlantic Subtropical High (NASH) western edge create a dipole that drives hydroclimate variability in the southeastern United States and Caribbean region. Southwest displacements suppress rainfall in the southern Caribbean. Northwest displacements drive the southeast United States and northern Caribbean drying. Projections for the 21st century suggest a more meridionally displaced NASH, which jeopardizes Caribbean island communities dependent on rain-fed aquifers. While recent study indicates that Atlantic and Pacific Ocean-atmosphere variability influenced the NASH during the instrumental period, little is known about NASH behavior and subsequent hydroclimate responses over longer timescales. To address this limitation, we developed a ∼6000-years long rainfall record through the analysis of calcite raft deposits archived within sediments from a coastal sinkhole in the northeast Bahamas (Abaco Island). Increased (decreased) calcite raft deposition provides evidence for increased (decreased) rainfall driven by NASH variability. To support this interpretation, we use simulations from the Community Earth System Model to improve the understanding of NASH behavior on timescales congruous with the reconstruction and which suggest an important role for the state of the Pacific Ocean. Furthermore, model simulations and a compilation of regional hydroclimate reconstructions reveal that the NASH-driven dipole dominates northern and southern Caribbeanmore »rainfall on centennial timescales. These results bring Holocene Caribbean hydroclimate variability into sharper focus while providing important context for present and future changes to regional climate. Additionally, this study highlights the need for improved future predictions of the state of the Pacific Ocean to best inform water scarcity mitigation strategies for at-risk Caribbean communities.« less
4. Late Miocene to Holocene high-resolution eastern equatorial Pacific carbonate records: stratigraphy linked by dissolution and paleoproductivity

   https://doi.org/10.5194/cp-15-1715-2019  

   Lyle, Mitchell ; Drury, Anna Joy ; Tian, Jun ; Wilkens, Roy ; Westerhold, Thomas ( January 2019 , Climate of the Past)

   Abstract. Coherent variation in CaCO₃ burial is a feature ofthe Cenozoic eastern equatorial Pacific. Nevertheless, there has been along-standing ambiguity in whether changes in CaCO₃ dissolution or changesin equatorial primary production might cause the variability. Sinceproductivity and dissolution leave distinctive regional signals, a regionalsynthesis of data using updated age models and high-resolution stratigraphiccorrelation is an important constraint to distinguish between dissolutionand production as factors that cause low CaCO₃. Furthermore, the newchronostratigraphy is an important foundation for future paleoceanographicstudies. The ability to distinguish between primary production anddissolution is also important to establish a regional carbonate compensationdepth (CCD). We report late Miocene to Holocene time series of XRF-derived (X-rayfluorescence) bulk sediment composition and mass accumulation rates (MARs) from easternequatorial Pacific Integrated Ocean Drilling Program (IODP) sites U1335,U1337, and U1338 and Ocean Drilling Program (ODP) site 849, and we also report bulk-density-derived CaCO₃ MARs at ODP sites 848, 850, and 851. We usephysical properties, XRF bulk chemical scans, and images along withavailable chronostratigraphy to intercorrelate records in depth space. Wethen apply a new equatorial Pacific age model to create correlated agerecords for the last 8 Myr with resolutions of 1–2 kyr. Large magnitudechanges in CaCO₃ and bio-SiO₂ (biogenic opal)more »MARs occurred withinthat time period but clay deposition has remained relatively constant,indicating that changes in Fe deposition from dust is only a secondaryfeedback to equatorial productivity. Because clay deposition is relativelyconstant, ratios of CaCO₃ % or biogenic SiO₂ % to clayemulate changes in biogenic MAR. We define five major Pliocene–Pleistocene low CaCO₃ % (PPLC) intervalssince 5.3 Ma. Two were caused primarily by high bio-SiO₂ burial thatdiluted CaCO₃ (PPLC-2, 1685–2135 ka, and PPLC-5, 4465–4737 ka),while three were caused by enhanced dissolution of CaCO₃ (PPLC-1, 51–402 ka, PPLC-3, 2248–2684 ka, and PPLC-4, 2915–4093 ka). Regional patterns ofCaCO₃ % minima can distinguish between low CaCO₃ caused by highdiatom bio-SiO₂ dilution versus lows caused by high CaCO₃dissolution. CaCO₃ dissolution can be confirmed through scanning XRFmeasurements of Ba. High diatom production causes lowest CaCO₃ %within the equatorial high productivity zone, while higher dissolutioncauses lowest CaCO₃ percent at higher latitudes where CaCO₃ production islower. The two diatom production intervals, PPLC-2 and PPLC-5, havedifferent geographic footprints from each other because of regional changesin eastern Pacific nutrient storage after the closure of the Central American Seaway.Because of the regional variability in carbonate production andsedimentation, the carbonate compensation depth (CCD) approach is onlyuseful to examine large changes in CaCO₃ dissolution.

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5. Late Holocene droughts and cave ice harvesting by Ancestral Puebloans

   https://doi.org/10.1038/s41598-020-76988-1  

   Onac, Bogdan P. ; Baumann, Steven M. ; Parmenter, Dylan S. ; Weaver, Eric ; Sava, Tiberiu B. ( December 2020 , Scientific Reports)

   Abstract Water availability for Native Americans in the southwestern United States during periods of prolonged droughts is poorly understood as regional hydroclimate records are scant or contradicting. Here, we show that radiocarbon-dated charcoal recovered from an ice deposit accumulated in Cave 29, western New Mexico, provide unambiguous evidence for five drought events that impacted the Ancestral Puebloan society between ~ AD 150 and 950. The presence of abundant charred material in this cave indicates that they periodically obtained drinking water by using fire to melt cave ice, and sheds light on one of many human–environment interactions in the Southwest in a context when climate change forced growing Ancestral Puebloan populations to exploit water resources in unexpected locations. The melting of cave ice under current climate conditions is both uncovering and threatening a fragile source of paleoenvironmental and archaeological evidence of human adaptations to a seemingly marginal environment.