6 research outputs found
Atlantic Meridional Overturning Circulation: Observed Transport and Variability
The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basin AMOC observational systems have been put in place to continuously monitor meridional volume transport variability, and in some cases, heat, freshwater and carbon transport. These observational programs have been used to diagnose the magnitude and origins of transport variability, and to investigate impacts of variability on essential climate variables such as sea surface temperature, ocean heat content and coastal sea level. AMOC observing approaches vary between the different systems, ranging from trans-basin arrays (OSNAP, RAPID 26°N, 11°S, SAMBA 34.5°S) to arrays concentrating on western boundaries (e.g., RAPID WAVE, MOVE 16°N). In this paper, we outline the different approaches (aims, strengths and limitations) and summarize the key results to date. We also discuss alternate approaches for capturing AMOC variability including direct estimates (e.g., using sea level, bottom pressure, and hydrography from autonomous profiling floats), indirect estimates applying budgetary approaches, state estimates or ocean reanalyses, and proxies. Based on the existing observations and their results, and the potential of new observational and formal synthesis approaches, we make suggestions as to how to evaluate a comprehensive, future-proof observational network of the AMOC to deepen our understanding of the AMOC and its role in global climate
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Pollutants from the Gulf War serve as water mass tracer in the Arabian Sea
In 1995, concentrations of the chlorofluorocarbon compound CFC‐12 in the outflow water from the Persian Gulf were 8–40 fold higher than normally caused by air‐sea gas exchange. At that time, the anomaly was restricted to the Gulf of Oman north of 20°N, while in 1998 the signal had spread southwestward to 12°N. The sources of this CFC‐12 input of about 6400 kg are most likely the fire extinguishers and solvents used during and after the Gulf War in 1991. This CFC‐12 signal is a new feature of the Persian Gulf Water (PGW) which can be used to track and quantify the spreading and dilution of PGW in the northern Indian Ocean. The contaminated PGW spreads southward with a mean velocity of 0.02–0.025 m s−1. At 20°N, the anomaly is diluted by a factor of more than two, and east of the island Socotra by a factor of four. A mean transport of less than 0.5·106 m³ s−1 is calculated for PGW assuming a mean dilution rate of 30% from the source signal in the Gulf of Oman to the western Arabian Sea