Abstract
Abstract. We present the distribution of water masses along the GEOTRACES-GA01 section during the GEOVIDE cruise, which crossed the subpolar North Atlantic Ocean and the Labrador Sea in the summer of 2014. The water mass structure resulting from an extended optimum multiparameter (eOMP) analysis provides the framework for interpreting the observed distributions of trace elements and their isotopes. Central Waters and Subpolar Mode Waters (SPMW) dominated the upper part of the GEOTRACES-GA01 section. At intermediate depths, the dominant water mass was Labrador Sea Water, while the deep parts of the section were filled by Iceland–Scotland Overflow Water (ISOW) and North-East Atlantic Deep Water. We also evaluate the water mass volume transports across the 2014 OVIDE line (Portugal to Greenland section) by combining the water mass fractions resulting from the eOMP analysis with the absolute geostrophic velocity field estimated through a box inverse model. This allowed us to assess the relative contribution of each water mass to the transport across the section. Finally, we discuss the changes in the distribution and transport of water masses between the 2014 OVIDE line and the 2002–2010 mean state. At the upper and intermediate water levels, colder end-members of the water masses replaced the warmer ones in 2014 with respect to 2002–2010, in agreement with the long-term cooling of the North Atlantic Subpolar Gyre that started in the mid-2000s. Below 2000 dbar, ISOW increased its contribution in 2014 with respect to 2002–2010, with the increase being consistent with other estimates of ISOW transports along 58–59° N. We also observed an increase in SPMW in the East Greenland Irminger Current in 2014 with respect to 2002–2010, which supports the recent deep convection events in the Irminger Sea. From the assessment of the relative water mass contribution to the Atlantic Meridional Overturning Circulation (AMOC) across the OVIDE line, we conclude that the larger AMOC intensity in 2014 compared to the 2002–2010 mean was related to both the increase in the northward transport of Central Waters in the AMOC upper limb and to the increase in the southward flow of Irminger Basin SPMW and ISOW in the AMOC lower limb.
Highlights
The 2014 GEOVIDE cruise consisted of two hydrographic sections: the seventh repetition of the OVIDE line from Lisbon (Portugal) to Cape Farewell (Greenland), and a section across the Labrador Sea from Cape Farewell to St
For the OVIDE line, the upper limb of the Atlantic Meridional Overturning Circulation (AMOC) is constituted by the Central Waters, the Subpolar Mode Waters (SPMW) of the Iceland Basin, Subarctic Intermediate Water (SAIW) and Mediterranean Water (MW), while the AMOC lower limb is constituted by the SPMW of the Irminger Sea (IrSPMW), Polar Intermediate Water (PIW), Labrador Sea Water (LSW), Iceland–Scotland Overflow Water (ISOW), Denmark Strait Overflow Water (DSOW) and North-East Atlantic Deep Water (NEADW) (García-Ibáñez et al, 2015)
We described and discussed the distribution of water masses along the GEOVIDE cruise (GEOTRACES-GA01 section), crossing the subpolar North Atlantic Ocean and the Labrador Sea in summer 2014
Summary
The 2014 GEOVIDE cruise consisted of two hydrographic sections: the seventh repetition of the OVIDE line from Lisbon (Portugal) to Cape Farewell (Greenland), and a section across the Labrador Sea from Cape Farewell to St. To provide a framework for interpreting the observed TEI distributions, in this work, we qualitatively assess the water mass distribution along the 2014 GEOTRACES-GA01 section through an extended optimum multiparameter (eOMP) analysis (Karstensen and Tomczak, 1998). We extend the study performed by García-Ibáñez et al (2015) for the 2002– 2010 OVIDE cruises, which described the distributions and temporal variations of the main water masses along the OVIDE line, and inferred the water mass transformations within the North Atlantic Subpolar Gyre. The assessment of the water mass volume transports based on dilutions of “pure” (OMP-based) water masses provides insights into the circulation features that are useful for areas of complex currents and water mass transformation, as in the subpolar North Atlantic (SPNA). We compare the water mass distribution and transport of the 2014 OVIDE line with the average water mass distribution and transport of the 2002–2010 OVIDE cruises (García-Ibáñez et al, 2015) and link the observed changes to major changes in the formation and circulation of water masses in the SPNA
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