Galochkina Mariya

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Galochkina
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Mariya
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  • Article
    Multispecies planktonic and benthic foraminiferal stable isotopes from North Atlantic subtropical site 558: Thermocline intensification during the mid-miocene climate transition
    ( 2023-04-25) Galochkina, Mariya ; Makarova, Maria ; Miller, Kenneth G. ; Browning, James V. ; Keating, Ronan S. ; Wright, James D.
    We reconstruct the subtropical North Atlantic water column structure during the Miocene Climate Optimum warming (MCO; 17–14.8 Ma) and the Middle Miocene Climate Transition cooling (MMCT; 14.8–12.8 Ma) by analyzing δ18O and δ13C in four species of foraminifera (surface dwellers Dentoglobigerina altispira and Trilobatus quadrilobatus, thermocline dweller Dentoglobigerina venezuelana, and benthic Planulina wuellerstorfi) from Site 558 (37.8°N). At the end of the MCO, δ18O of surface and thermocline dwellers increased by >1‰, suggesting at least 2°C cooling in the upper ocean as ice growth increased global δ18Osw by ∼0.5‰. The difference in δ18O values between thermocline and surface-dwelling species increased during the MMCT, coinciding with the development of a largely permanent East Antarctic Ice Sheet, and persisted into the Late Miocene. We interpret this increase in vertical δ18O gradient as a strengthening of the thermocline due to intensification of subtropical gyre circulation in response to the MMCT cooling.
  • Article
    Coral Sr-U Thermometry tracks ocean temperature and reconciles Sr/Ca discrepancies caused by Rayleigh Fractionation
    (American Geophysical Union, 2023-07-14) Galochkina, Mariya ; Cohen, Anne L. ; Oppo, Delia W. ; Mollica, Nathaniel Rust ; Horton, Forrest
    Understanding climate change at the spatiotemporal scales necessary to improve climate projections requires proxy records that complement sparse and often contradictory observational temperature data sets. Massive long-lived corals have tremendous potential in this regard, continuously recording information about ocean conditions as they grow. Nevertheless, extracting accurate ocean temperatures from corals is challenging because factors other than temperature influence skeletal chemistry. Here, we tested the ability of the coral Sr-U thermometer to accurately capture annual sea surface temperatures (SSTs) in the subtropical Atlantic, where year-to-year temperatures vary by ∼1°C. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), we generated sufficient U/Ca – Sr/Ca pairs from a slow-growing (1−2 mm/yr) Siderastrea siderea coral to calculate annual Sr-U values. With the fine-scale spatial resolution attained using the laser, skeleton accreted during both fast and slow growing times of the year was represented in our sampling. The resulting 30-year-long Sr-U record tracked the amplitude and timing of annual SST to within ±0.2°C of observations (r = −0.71), whereas the Sr/Ca record did not (r = 0.23). Furthermore, Sr-U corrected for Sr/Ca offsets among adjacent skeletal elements approximately 1 mm apart. These offsets are equivalent to differences of 2–3°C if typical Sr/Ca–SST calibrations are applied. Our observations indicate that Sr-U can accurately constrain decadal-to-multidecadal variability and secular SST trends in regions where this information is urgently needed.