The Atlantic Meridonial Overturning Circulation (AMOC) in the North Atlantic Ocean (NAO) plays a major role in earth’s climate and climate change. A key element of the AMOC is deep convection, which is still not fully understood. One of the unknowns is where water is exchanged between the boundary current and the regions where deep convection can occur. This is important for models to know where deep waters are formed and where they are transported to. This study focuses on the Irminger Sea (IRS), a sub-sea of the NAO. The interior of this sub-sea is a known area where deep convection can occur. Using data from the Argo Float Program, a analysis was conducted to investigate exchanges of water between the boundary current of the IRS and the area where deep convection can occur. The entries and departure locations of the Argo floats are collected and statistically compared. Furthermore, seasonality difference between winter and summer months are compared using the Mann-Whitney U-Test. Lastly, the internal pathways water takes within the interior area are analysed, by tracking where a float enters the interior area and where it afterwards leaves the area. The results show water takes many different pathways in and out of the interior area and the pathways taken within the area show the expected cyclonic pattern. There were no clear differences between summer and winter months, except in the northern part of the interior area, where in winter a clear south-western current is present, but not in summer. Future studies on the exchange between the boundary current and the interior area can use these results as an indication that the exchange happens all around the area, but the water does follow a cyclonic pattern. ... Read more

The Earth’s climate is changing, due to global warming, impacting the ocean circulation around the world. As the ocean circulation distributes large amounts of energy around the world, this can alter climate drastically if changed. The Atlantic Meridional Overturning Circulation (AMOC) is a fundamental ocean component to comprehend climate change and further investigation enhances our capacity to predict it. The AMOC plays a pivotal role in regulating the ocean heat transport within the North Atlantic Ocean, influencing the climates of North America and Europe. This study centers its attention on the Sub-Polar Gyre (SPG), a critical region where the AMOC activity peaks. Within this region, this study aims to get a better understanding of the overturning dynamics of the SPG, on a seasonal and annual time scale. To achieve this, the reanalysis model GLORYS12 is used, which offers a detailed simulation of ocean dynamics spanning the period from 1993 to 2020. With its high-resolution, eddy-resolving capabilities, GLORYS12 is particularly well-suited for capturing the nuanced small-scale overturning processes associated with the AMOC. From these model data, the overturning is calculated from alongstream changes in boundary current transport divided in density classes. The analysis is performed for the entire SPG by dividing it into its major basins: the Iceland Basin, Irminger Sea, and Labrador Sea. Subsequently, the boundary currents of the SPG are further subdivided into seventeen individual segments, providing insights into how overturning dynamics vary along the SPG. The results reveal that the mean overturning strength in the SPG for 1993-2020 is 23.8 Sverdrups (106 m3/s (Sv)). The distribution in overturning strength between the basins is 41%, 29%, and 30% for the Iceland Basin, Irminger Sea, and Labrador Sea respectively. Furthermore,
the results shows overturning occurs at increasingly higher densities, the further west you go. Each basin displays a pronounced seasonal pattern, with maximum overturning occurring in March and the minimum in September. On an inter-annual time scale, the overturning strength in both the Iceland Basin and Irminger Sea exhibits a decreasing trend of -0.04 and -0.02 Sv/year respectively, whereas the Labrador Sea has an increasing trend of 0.02 Sv/year over 1993-2020. A further division in shorter segments yields large spatial differences in overturning, both in overall strength and the distribution over density classes. However, these outcomes are less robust as flows are highly variable and numerical errors associated with the overturning calculations become more prominent. This also raises questions about the reliability of the assessment
of overturning along segments from observations to determine the local overturning dynamics. In conclusion, this study leverages GLORYS12 for a detailed basin and segmented analyses to offer a comprehensive understanding of the AMOC within the SPG. The findings provide valuable insights into the AMOC’s long-term behavior, seasonal variations, annual trends, and high spatial variability. Using this increased understanding, future research can improve on why the AMOC behaves in the observed way, by analyzing the overturning dynamics sensitivity to oceanic and atmospheric conditions ... Read more