Oceanic transport of subpolar climate signals to mid-depth subtropical waters

Abstract

The spatial distributions of certain sea-surface properties, such as temperature, fluctuate on timescales from months to decades and in synchrony with the main regional atmospheric patterns comprising the global climate system 1 . Although it has long been assumed that the ocean is submissive to the dictates of the atmosphere, recent studies raise the possibility of an assertive, not merely passive, oceanic role in which water-mass circulation controls the timescales of climate fluctuations 2-6 . Previously held notions of the immutability of the physical and chemical characteristics of deep water masses are changing as longer time series of ocean measurements indicate that the signatures of varying sea-surface conditions are translated to deep waters 4,7 . Here we use such time-series measurements to track signals 'imprinted' at the sea surface in the North Atlantic Ocean's subpolar Labrador Basin into the deep water of the subtropical basins near Bermuda, and infer an approximately 6-year transit time. We establish a geographic and temporal context for a portion of the long-term warming trend reported for mid-depth subtropical waters over the past 40 or so years 8,9 , and we predict that waters at these depths will continue to cool well into the next decade.

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

“…Consequently, its formation, spreading, and decay have been well described recently (Lazier et al, 2002;Yashayaev, 2007;Yashayaev et al, 2007aYashayaev et al, , 2007bFalina et al, 2007). By extending the data from the surveys of the AR7 section in the central Labrador Sea with historic oceanographic data from 1960 onwards Yashayaev (2007) and Curry et al (1998) were able to show that the temperature-salinity characteristics of LSW mainly varied on a multi-decadal time scale ($ 50 years), with a warm and saline period in the late 1960s and a cold and fresh phase in the mid-1990s. In this paper we repeat that effort, including oxygen profiles, and extend it to other basins, the central Irminger Sea and western Iceland Basin, and to the year 2009.…”

“…The potential density anomaly, relative to a reference pressure of 1500 dbar, g 1.5 , has been derived from the temperature and salinity profiles and is used as density parameter. Similar data sets of only temperature and salinity profiles were constructed by Yashayaev (2007) and Curry et al (1998) for the Labrador Sea.…”

Coherent surface‐subsurface fingerprint of the Atlantic meridional overturning circulation

“…[9] The weakening of the AMOC during the 70-80's inferred from the observed Tsub PC1 (Figure 2c) lagged the observed reductions of Labrador Sea deep convection induced by Great Salinity Anomalies events at the early 70's and 80's [Dickson et al, 1988;Curry et al, 1998] by several years. During the recent decade, the peak of the AMOC at 1998 inferred from observed PC1s of Tsub and SSH (Figure 2c) lags the observed peak of Labrador Sea deep convection around 1994 [Yashayaev et al, 2007] by several years.…”

Tracer distributions and deep circulation in the western tropical Atlantic during CITHER 1 and ETAMBOT cruises, 1993–1996

“…Stream waters [Pickart, 1992;Spall, 1996] and then with the Mediterranean Water (MW) through recirculation cells and eddies [Reid, 1994;Curry et al, 1998]. In the subtropics and tropics the CFC maximum is associated with a salinity maximum characterizing the MW (Figure 5a) Although CFC and oxygen both enter the ocean in high latitudes through ventilation processes, their distributions are very different at the UNADW level (Figures 2a, 3a, 4a, and 7a).…”