Atlantic Meridional Overturning Circulation at 14.5° N in 1989 and 2013 and 24.5° N in 1992 and 2015: volume, heat, and freshwater transports

Abstract

Abstract. The Atlantic Meridional Overturning Circulation (AMOC) is analyzed by applying a box inverse model to hydrographic data from transatlantic sections along 14.5

Interannual Variability of Antarctic Intermediate Water in the Tropical North Atlantic

“…As shown in Argo data, on interannual timescales, the AAIW salinity variability has a peak to trough magnitude of 0.04 in the tropical North Atlantic. This magnitude is comparable to that found in analyses of property changes at intermediate depth determined from repeated hydrographic surveys (Arbic & Owens, ; Curry et al, ; Fu et al, ). Traditional analysis of water masses based on hydrographic sections cannot account for the interannual variability of salinity, since the occupation of the sections is usually decades apart.…”

“…The Hovmoeller diagram shows a salinification trend of AAIW between 1985 and 2005, followed by a strong negative anomaly. The salinification of AAIW in the tropical North Atlantic in GECCO2 is consistent with the estimates based on hydrographic data (Fu et al, ; Schmidtko & Johnson, ), though the salinification trend in GECCO2 (3 × 10¯ 3 year ‐1 ) is somewhat stronger than the trend (about 1 × 10¯ 3 year ‐1 ) estimated by Schmidtko and Johnson (). The stronger salinification trend in GECCO2 may result from the assimilation procedure, which alters the solution of the model toward all the available data.…”

“…This may be associated with the eastward advection of AAIW anomalies by the weak eastward current bands observed between 12 and 14°N (Brandt et al, ; Hahn et al, ; Peña‐Izquierdo et al, ). In the Atlantic, long‐term warming and salinification of AAIW have been shown in the observational data (Fu et al, ; Schmidtko & Johnson, ) and in GECCO2. These long‐term water mass anomalies were attributed to changes in the atmospheric conditions in the AAIW formation region and an enhanced Aguhlas leakage associated with variations in the southern annular mode (Lübbecke et al, ; Schmidtko & Johnson, ), and to a weaker transport in the intermediate layer, hence less fresher AAIW from the South Atlantic (Fu et al, ).…”

“…A number of studies have investigated the salinity and temperature changes in the intermediate layer of the Atlantic Ocean (Arbic & Owens, ; Fu et al, ; McCarthy et al, ; Sarafanov et al, ; Schmidtko & Johnson, ). Consistently, these studies revealed that during the last decades, AAIW became warmer and lighter in the South Atlantic, while it became warmer and more saline in the tropical North Atlantic.…”

“…However, the salinification of AAIW in the tropical Atlantic does not seem to align with an enhanced hydrological cycle in the global warming scenario (e.g., Held & Soden, ). Fu et al () suggested that instead a weaker northward transport in the intermediate layer could be responsible for the observed AAIW salinification at 14.5°N in the Atlantic, highlighting the importance of water mass property changes along the spreading path due to entrainment and mixing with surrounding waters.…”