ALBERT

Description: PREFCLIM is a mixed-layer climatology for the Eastern Tropical Atlantic. The climatology contains a high-resolution (0.25 degrees) monthly-mean mixed-layer hydrography (mixed-layer depth, temperature, salinity), and coarse-resolution (2.5 degrees) estimates of the mixed-layer heat and salt balance, as well as of near-surface velocities and of air-sea fluxes. All existing hydrographic products of the region were hampered by the sparse availability of near-shore data owned by the West-African coastal countries, which could, however, be included in the new climatology.

Description: Two Teledyne RDI Ocean Surveyor systems with 38 and 75 kHz transmission frequency were used. Data was processed with a software package developed at GEOMAR following the GO-SHIP standards (Firing and Hummon, 2010). The data was subsequently averaged over one minute intervals and converted to a NetCDF based format.

Description: This dataset is a collection of moored velocity data used in the study “Sources and pathways of intraseasonal meridional kinetic energy in the equatorial Atlantic Ocean” (Körner et al., 2022) to analyze the representation of meridional intraseasonal velocity variability in a general circulation model. The observational velocity data were collected at five different locations along the equator. At 0°N, 35°W velocity data were collected by single-point current meters in four different depths from October 1992 until May 1994. Between August 2004 and June 2006 an acoustic Doppler current profiler (ADCP) and single-point current meters collected data at 0°N, 35°W. Moorings at 0°N, 23°W provide velocity measurements from December 2001 to June 2021 (apart from a period from December 2002 to February 2004 when no mooring was in place). At 0°N, 10°W velocity data were collected between May 2003 to March 2019 using ADCPs and single-point current meters. However, the mooring was not consecutively installed leading to data gaps of up to two years. Between 2007 and 2011 ADCPs recorded velocity data at 0°N, 0°E.

Description: The upper-ocean circulation of the tropical Atlantic is a complex superposition of thermohaline and wind-driven flow components. The resulting zonally- and vertically-integrated upper-ocean meridional flow is referred to as the upper branch of the Atlantic Meridional Overturning Circulation (AMOC) - a major component and potential tipping element of the global climate system. We investigate the tropical part of the northward AMOC branch, i.e. the return flow covering the upper 1,200 m, based on Argo data and repeated shipboard velocity measurements. The western boundary mean circulation at 11°S is realistically reproduced from high-resolution Argo data showing a remarkably good representation of the vertical structure of meridional velocity and the volume transport of water mass layers when compared to results from direct velocity measurements along a repeated ship section. Thus, we extend the analysis to the inner tropical Atlantic. Within the AMOC return flow, a diapycnal upwelling of central water into the thermocline layer of ~2 Sv is derived between 11°S and 10°N which is about half the magnitude of previous estimates, likely due to improved horizontal resolution. The mean strength of the AMOC return flow is ~16 Sv across 11°S and 10°N. At 11°S, northward transport is concentrated at the western boundary where the AMOC return flow enters the tropics at all vertical layers above 1,200 m. At 10°N, northward transport is observed both at the western boundary and in the interior predominantly in the surface and intermediate layer indicating recirculation and transformation of thermocline and central water within the tropics.

Description: The tropical Angolan upwelling system is a highly productive ecosystem with a distinct seasonal cycle in surface temperature and primary production. The lowest sea surface temperature, strongest cross-shore temperature gradient, and maximum productivity occur in austral winter when seasonally prevailing upwelling favorable winds are weakest. A multi cruise dataset of microstructure profiles collected between 2013 and 2022 in the tropical Angolan upwelling system was used to analyze the importance of mixing for cooling of the mixed layer. The data were collected during six cruises on board of the R/V Meteor. The results show that cooling due to turbulent heat fluxes at the base of the mixed layer is an important cooling term. This turbulent cooling, that is strongest in shallow shelf regions, is capable of explaining the observed negative cross-shore temperature gradient.