838 / 2024-09-19 16:13:13

Upper ocean instability in subpolar North Atlantic and its implications for deep water formation during interglacials

marine isotope stage 11,Paleoceanography,stable isotope,AMOC

In this multiproxy study, we used new isotopic data on planktonic foraminifera to highlight the strong instability that characterized surface conditions in the Iceland Basin during Marine Isotope Stage 11 (MIS 11). We produced new carbon and oxygen isotope data on the planktonic species Neogloboquadrina incompta and Turborotalita quinqueloba, foraminifera-bound nitrogen isotope data on Neogloboquadrina incompta, and calcareous nannofossil data at coring site IODP U1314. The multiproxy record displays two distinct upper ocean regimes: a relatively stable pre-climate optimum and an unstable post-climate optimum with high amplitude variations in nutrient utilization and seasonality proxies, and strong enrichment in oxygen isotopes suggesting colder and/or saltier upper waters. The latter regime was concomitant with a resurgence in ice-rafted debris. Interestingly, this instability is not observed in cores affected by the North Atlantic Current. Moreover, deep water ventilation is increasing at locations influenced by the subpolar gyre (e.g., the Iceland Basin and Labrador Sea), while it decreases in the North Atlantic (Ocean Drilling Program Site 980). The evidence presented here indicates that deep-water formation was dynamic or unstable throughout MIS 11, and that peak periods of deep-water formation varied across high latitude North Atlantic basins, depending on the prevailing surface conditions in each region. This finding suggests that reconstructing deep-water formation and ventilation processes using data from a single site may not provide a complete picture. Instead, a more comprehensive approach that accounts for the interconnectivity and interactions between different components of the overturning circulation system is necessary to accurately estimate deep-water formation and ventilation during past interglacial.