Estimating oceanic transports of volume, heat, carbon, and freshwater is fundamental to understanding the ocean’s role in the changing climate system. Unique in this context is the Atlantic Meridional Overturning Circulation (AMOC) that comprises a net northward transport of relatively warm water at depths of ≲1 km throughout the Atlantic basin, compensated at depths of ≳1–5 km by a colder net southward return flow (NADW).
While in-situ measurements, such as the RAPID array at 26.5°N, are considered the 'gold standard' to monitor changes in the AMOC, measurements at many latitudes and the detection of e.g. basin-wide modes are not feasible with such costly arrays.
However, variations in the geostrophic part of the AMOC are to a good degree described by variations in NADW transport and therefore in principle accessible through ocean bottom pressure measurements and possibly future satellite gravimetry missions.

Here, we investigate the connection between changes in the NADW transport and associated variations in bottom pressure along the western continental slope and shelf in the North and South Atlantic in the regional high-resolution ocean model VIKING20X provided by GEOMAR. We assess to what degree the transport variations can be inferred from bottom pressure signatures alone, limitations of the approach and especially how such signatures could be implemented into a future iteration of the ESA Earth-System-Model which is commonly used in simulation studies for satellite gravimetry. This would allow the inclusion of these transport-related OBP changes in dedicated simulation studies in preparation for future satellite gravimetry missions.

How to cite: Shihora, L., Martin, T., Hans, A. C., Hummels, R., and Dobslaw, H.: Connecting NADW transports to ocean bottom pressure variations with the high-resolution ocean model VIKING20X, GRACE/GRACE-FO Science Team Meeting, Potsdam, Germany, 8–10 Oct 2024, GSTM2024-14, https://doi.org/10.5194/gstm2024-14, 2024.

Changes in sea level can arise from steric and manometric effects, with the partition between them depending on depth and other dynamical factors. In the shallow coastal oceans, the manometric term associated with bottom pressure variations is expected to become larger than the steric term, but a quantitative analysis of this breakdown remains missing. In this work, we use gridded monthly bottom pressure estimates from GRACE and GRACE-FO, together with temperature and salinity data compiled under the World Ocean Atlas 2023, to quantify manometric and steric contributions to the mean seasonal cycle in sea level across the coastal zone, as observed by tide gauges and satellite altimeters.

Focusing on depths shallower than 2000 m and global median values, the sum of the estimated steric and manometric terms can explain approximately 65% of the annual variance and 40% of the semiannual variance in the sea level observations. We identify several regions, e.g., the Australian seaboard, where the seasonal sea level budget is not closed, pointing to data noise, limited horizontal resolution, or residual leakage errors in the GRACE/-FO solutions. Indeed, comparisons of sea level, steric and manometric terms calculated based on different products suggest sizable uncertainties in the available estimates of the mean seasonal cycle in coastal bottom pressure. For most regions with a sufficiently tight budget closure, we find that whilst the importance of the manometric term generally increases with decreasing water depth, steric contributions are non-negligible near coastlines, especially at the annual frequency.

How to cite: Ponte, R. and Schindelegger, M.: Role of bottom pressure in the seasonal cycle of coastal sea level, GRACE/GRACE-FO Science Team Meeting, Potsdam, Germany, 8–10 Oct 2024, GSTM2024-10, https://doi.org/10.5194/gstm2024-10, 2024.

Three decades of satellite radar altimetry have provided an important global mean sea level change record. Validation of that record against other independent data is critical. Sea level rise has two primary causes: steric expansion of the oceans due to temperature and salinity changes, observed globally since 2005 by the Argo float network, and ocean mass change, uniquely and critically observed by GRACE and GRACE-FO since 2002. The globally averaged sum of Argo steric expansion and GRACE(-FO) ocean mass can be compared directly to the radar altimetry record, a comparison that is widely referred to as the Sea Level Budget, and numerous groups have assessed this comparison for over a decade. Recent improvements to Jason-3 wet troposphere modelling has helped show closure of the budget through around 2020, but growing misclosure of the two records in the years since remains unexplained. Our most recent estimates of the 2005-2024 trend in global mean sea level, presented at the 30 Years of Progress in Radar Altimetry Symposium in September 2024, show sea level rise of 3.80 mm/year from altimetry and 3.56 mm/year from GRACE+Argo. In this work, we more deeply investigate this recent misclosure. After first establishing a new unified ocean mask for all three datasets, we examine the budget over subsets of the global ocean and show that the disagreement cannot be explained by differences in any one small portion of the ocean. We then investigate and compare ocean mass changes in Earth’s gravity from GRACE(-FO) and Altimetry-minus-Argo and show that disagreements between these records at long spherical wavelengths can explain differences in the recovered trends in global mean sea level.

How to cite: Croteau, M., Beckley, B., Loomis, B., Ray, R., and Lemoine, F.: Assessing causes of recent sea level budget misclosure, GRACE/GRACE-FO Science Team Meeting, Potsdam, Germany, 8–10 Oct 2024, GSTM2024-19, https://doi.org/10.5194/gstm2024-19, 2024.

The GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Gravity Recovery and Climate Experiment - Follow On) satellite missions have enabled global monitoring of mass transport within the Earth's system, leading to unprecedented advances in understanding the global water cycle in the context of a changing climate. Over the past two decades (2002–2022), the combination of satellite gravimetry with altimetry data has allowed us to monitor the change in the ocean heat content (OHC) which is the main reservoir to store the excess of energy accumulated in the Earth system due to human activities. From the global OHC estimate, the Earth's energy imbalance (EEI: +0.8 W/m²) was derived with high accuracy (±0.16 W/m² within a 90% confidence interval). The primary source of uncertainty in our geodetic EEI estimate arises from the post-processing of satellite gravity measurements, which has been rigorously evaluated using an ensemble approach. Independent comparisons with the Clouds and the Earth's Radiant Energy System (CERES) mission further highlighted the critical importance of post-processing corrections for the detection of realistic changes in EEI at interannual and decadal time scales. These findings underscore the need to enhance consistency between satellite altimetry and gravimetry measurements, particularly concerning geocenter corrections. Additionally, investigations into the spatial and temporal variations in OHC have shown that post-processing corrections applied to satellite gravimetry data, such as leakage correction, are crucial for accurately capturing temporal variations in EEI. Better-informed decisions regarding the selection of post-processing corrections can be made by leveraging the redundancy of the ocean and climate monitoring system to ensure the closure of the energy and sea level budgets at the global and regional scales.

How to cite: Pfeffer, J., Fraudeau, R., Meyssignac, B., Blazquez, A., Fourest, S., Marti, F., Ablain, M., Larnicol, G., Restano, M., Sabia, R., Dibarboure, G., and Benveniste, J.: Assessing Spatial and Temporal Variations in the Ocean Heat Content and Earth Energy Imbalance from Space Geodetic Data , GRACE/GRACE-FO Science Team Meeting, Potsdam, Germany, 8–10 Oct 2024, GSTM2024-56, https://doi.org/10.5194/gstm2024-56, 2024.