Last Deglacial Environmental Change in the Tropical South Pacific From Tahiti Corals

• Published in: Paleoceanography and Paleoclimatology 2024-02, Vol.39 (2), p.n/a
• Main Authors: Knebel, Oliver, Felis, Thomas, Asami, Ryuji, Deschamps, Pierre, Kölling, Martin, Scholz, Denis
• Format: Article
• Language: English
• Subjects: Annual variations; Archives; Carbon 13; Chemical composition; Climate; Climatic conditions; Convergence; Convergence zones; Coral growth; coral reefs; Corals; deglacial; Deglaciation; Drilling; Earth movements; Earth orbits; Earth Sciences; Environmental changes; Environmental conditions; Expeditions; Glacial periods; Growth rate; Ice volume; Interglacial periods; IODP; Meltwater; meltwater pulse 1A; Mixed layer; Mixed layer depth; Northern Hemisphere; paleoclimate; Porites; Rainfall; Runoff; Salinity; Sciences of the Universe; Sea surface; Sea surface temperature; Seasonal variation; Seasonal variations; Seasonality; Strontium; Surface temperature; Tahiti; Younger Dryas
• ISSN: 2572-4517; 2572-4525; 2572-4525; 1944-9186
• DOI: 10.1029/2022PA004585

On glacial‐interglacial time scales, changes in the Earth's orbital configuration control climate seasonality and mean conditions. Tropical coral skeletons can be sampled at a sufficient resolution to reconstruct past seasonality. Here, last deglacial Porites skeletons from Integrated Ocean Drilling Program Expedition 310 to Tahiti are investigated and, supported by a modern calibration, monthly resolved time series in geochemical proxies (Sr/Ca, δ18O, δ13C) are constructed. For most of the deglaciation, Sr/Ca seasonality was similar to modern (0.139 ± 0.010 mmol mol−1; 2.8 ± 0.2°C) reflecting the small change in insolation seasonality. However, during the Younger Dryas, high values in Sr/Ca seasonality (0.171 ± 0.017 mmol mol−1; 3.4 ± 0.3°C) suggest a reduced mixed layer depth and enhanced influence of the South Pacific Subtropical Gyre due to South Pacific Convergence Zone (SPCZ) inactivity. Furthermore, high amplitudes in Younger Dryas skeletal δ18O (0.40 ± 0.22 ‰) and δ13C (0.86 ± 0.22 ‰) seasonality compared to modern (δ18O = 0.29 ± 0.08 ‰; δ13C = 0.27 ± 0.08 ‰) point to elevated winter‐summer discrepancies in rainfall and runoff. Mean coral Sr/Ca variability suggests an influence of Northern Hemisphere climate events, such as the Younger Dryas cooling (+0.134 ± 0.012 mmol mol−1;−2.6 ± 0.2°C), or the Bølling–Allerød warming (+0.032 ± 0.040 mmol mol−1; −0.6 ± 0.4°C). Deglacial mean coral Δδ18O (δ18Oseawater contribution to skeletal δ18O), corrected for the ice volume effect, was elevated pointing to more saline, thus dryer conditions, likely due to a northward migration of the SPCZ. Seasonal cycles in coral δ13C were likely caused by variations in linear extension rates that were reduced during the last deglaciation (1.00 ± 0.6 cm year−1) compared to today (1.6 ± 0.3 cm year−1). Plain Language Summary Changes in the Earth's movement around the sun are the primary cause of changes in the annual cycle and annual mean of environmental conditions during the last glacial‐interglacial periods. Distinct from most climate archives, the annual bands of coral skeletons can be sampled at a monthly resolution that allows for reconstructions of past seasonal cycles. In this study, the chemical composition of coral skeletons from the genus Porites that grew during the last deglaciation at Tahiti (∼15,000–9,000 years ago) was analyzed to infer seasonal variations and mean conditions in past sea surface temperature and salinity. Prior to application, the methods were