Close con­nectiv­ity within the North At­lantic Cur­rent sys­tem iden­ti­fied

An acous­tic cur­rent meter, built into a moor­ing buoy be­ing pre­pared for de­ploy­ment in the At­lantic. The ocean cur­rent is meas­ured with these in­stru­ments.
Photo Credit: MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences, Uni­versity of Bre­men, D. Kieke

Long-term com­par­at­ive study re­veals par­al­lels between time series from Flor­ida and New­found­land

Re­search­ers from the Uni­versity of Bre­men and the Fed­eral Mari­time and Hy­dro­graphic Agency have com­pared long-term data on the At­lantic Me­ri­di­onal Over­turn­ing Cir­cu­la­tion from two dif­fer­ent lat­it­udes and dis­covered a stat­ist­ical cor­rel­a­tion. Their aim was to in­vest­ig­ate how the At­lantic Me­ri­di­onal Over­turn­ing Cir­cu­la­tion has de­veloped over a period of 25 years, based on moored ob­ser­va­tion sta­tions. These data will help to re­fine cli­mate mod­els in the fu­ture. The study has been pub­lished in the journal Geophysical Research Letters.

In ad­di­tion to wind, tem­per­at­ure and sa­lin­ity are the driv­ing forces of ocean cur­rents in the North At­lantic. They trans­port warm, salty wa­ter from the sub­trop­ical re­gions north­ward to the colder, lower-sa­lin­ity areas. Like the wind-driven Gulf Stream, these cur­rents are com­pon­ents of the At­lantic Me­ri­di­onal Over­turn­ing Cir­cu­la­tion (AMOC). Be­cause of the im­mense amount of heat it trans­ports, the AMOC is an im­port­ant part of the global cli­mate sys­tem. For ex­ample, it in­flu­ences re­gional pre­cip­it­a­tion as well as strong trop­ical storms, and acts as a re­mote heat­ing sys­tem for Europe’s cli­mate.

Schematic representation of the most important North Atlantic currents. Red (blue) arrows show the upper (deep) circulation paths. The acronyms indicate the positions of the North Atlantic Current (NAC) and the Eastern Boundary Current (EBC). The black lines show the transport lines of the observatory arrays.
Graphic Credit: MARUM – Center for Marine Environmental Sciences, University of Bremen; S. Wett.

Long-term stud­ies help to doc­u­ment changes and re­fine the math­em­at­ical mod­els of fu­ture cli­mate change. Mod­el­ling stud­ies in­dic­ate that, in a warm­ing world, the ex­pec­ted weak­en­ing of the AMOC could have an im­pact on re­gional tem­per­at­ure or pre­cip­it­a­tion pat­terns. Long-term ob­ser­va­tion sys­tems have been in place, for ex­ample, at 26 de­grees north lat­it­ude between the east side of Flor­ida and the west coast of Africa. For the first time, re­search­ers from Bre­men and Ham­burg have com­pared these data, cov­er­ing a period of 25 years, with those from an ob­ser­va­tion sys­tem to the north at 47 de­grees north between New­found­land and France.

“We see a stat­ist­ical con­nec­tion,” says first au­thor Si­mon Wett of MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences and the In­sti­tute of En­vir­on­mental Phys­ics at the Uni­versity of Bre­men. “There are par­al­lels between the data from the two ob­ser­va­tion sys­tems. Parts of what we ob­serve in the data from our sys­tem dur­ing this ex­ten­ded time period, we also see a few months later at the 26-de­gree sta­tions."

The long-term study, ex­tend­ing over the en­tire span of the At­lantic basin, is based on data from ar­rays of moor­ings that col­lect meas­ure­ment para­met­ers both near the sur­face of the ocean as well as at greater depths within the wa­ter column. These in­clude, for ex­ample, the sa­lin­ity, wa­ter tem­per­at­ure, and strength of the cur­rent. The moor­ings at 47°N were in­stalled as a co­oper­at­ive pro­ject between the Uni­versity of Bre­men and the Fed­eral Mari­time and Hy­dro­graphic Agency (BSH).

The re­search­ers are con­vinced that a long time series provides a bet­ter found­a­tion for fu­ture mod­els to real­ist­ic­ally sim­u­late the AMOC. “Of course, we need to con­tinue to mon­itor the AMOC in or­der to make long-term as­sess­ments and fu­ture pro­gnoses,” says Si­mon Wett. A long-term trend of strength­en­ing or weak­en­ing of the cur­rent could not be iden­ti­fied from the study by Wett and his col­leagues, which cov­ers the past quarter of a cen­tury.

Published in journal: Geophysical Research Letters

Source/Credit: MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences

Reference Number: es101223_01

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