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The Atlantic Meridional Overturning Circulation (AMOC) is the large-scale system of ocean currents that contributes to a moderate climate in northern Europe. AMOC transports vary on a range of time scales, from daily to centennial. Up to now, the role of atmospheric noise in subseasonal and intra-annual AMOC variations remains unclear. The current study describes a modeling experiment planned to reveal the importance of mesoscale winds around the southern tip of Greenland, named Tip Jets, in AMOC variability. Although Tip Jets are known to affect the heat content of the North Atlantic Subpolar Gyre intensifying deep water formation in the Irminger Sea, the open question is how this change in deep convection intensity evinces in the AMOC subseasonal variations. The experiment will be performed using the high-resolution (~10 km) Parallel Ocean Program (POP) model. Therefore, we constructed the composite Tip Jet forcings using daily ERA5 (25 km, December-March: DJFM, 1969-2022) momentum, and total surface heat fluxes, which will be added to the climatology to investigate the possible response of the AMOC system. Tip Jet events were defined as 10% strongest westerly winds in the region 59-60.5° N, 38-48° E. Forcings will be applied to the area outlined by the 30% contour of the greatest heat loss associated with Tip Jets. The described experiment is expected to disentangle the relative influence of momentum and heat Tip Jet forcing on the deep water formation and intra-annual AMOC variability., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

[1] We present an almost 3 year long time series of shell fluxes and oxygen isotopes of left-coiling Neogloboquadrina pachyderma and Turborotalita quinqueloba from sediment traps moored in the deep central Irminger Sea. We determined their response to the seasonal change from a deeply mixed water column with occasional deep convection in winter to a thermally stratified water column with a surface mixed layer (SML) of around 50 m in summer. Both species display very low fluxes during winter with a remnant summer population holding out until replaced by a vital population that seeds the subsequent blooms. This annual population overturning is marked by a 0.7‰ increase in δ18O in both species. The shell flux of N. pachyderma peaks during the spring bloom and in late summer, when stratification is close to its minimum and maximum, respectively. Both export periods contribute about equally and account for >95% of the total annual flux. Shell fluxes of T. quinqueloba show only a single broad pulse in summer, thus following the seasonal stratification cycle. The δ18O of N. pachyderma reflects temperatures just below the base of the seasonal SML without offset from isotopic equilibrium. The δ18O pattern of T. quinqueloba shows a nearly identical amplitude and correlates highly with the δ18O of N. pachyderma. Therefore T. quinqueloba also reflects temperature near the base of the SML but with a positive offset from isotopic equilibrium. These offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species. In the Irminger Sea the species consistently show a contrast in their flux timings. Their flux-weighted Δδ18O will thus dominantly be determined by seasonal temperature differences at the base of the SML rather than by differences in their depth habitat. Consequently, their sedimentary Δδ18O may be used to infer the seasonal contrast in temperature at the base of the SML.