Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

Goodkin, Nathalie F.; Druffel, Ellen R. M.; Hughen, Konrad A; Doney, Scott C.

doi:10.1038/ncomms1811

Cited by 14 publications

(39 citation statements)

References 30 publications

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“…Bermuda data are from Druffel [, ] and Goodkin et al . [], Florida data are from Druffel [], and Puerto Rico data are from Kilbourne et al . [].…”

Section: Resultsmentioning

confidence: 99%

“…Florida data are from Druffel []; Bermuda includes data from Druffel [, ] and Goodkin et al . []. Puerto Rico data are from Kilbourne et al .…”

Section: Resultsmentioning

confidence: 99%

“…The source of water entering into the subsurface Caribbean and the Bahamas explains the close agreement between the Bermuda record and the Bahamas sclerosponge. Corals from Bermuda record the 14 C signature of the western subtropical North Atlantic before the water is transported to the eastern side of the basin as part of the gyre circulation [ Druffel , ; Druffel , ; Goodkin et al ., ]. In the eastern subtropical Atlantic, the water meets the seasonal outcrops of the isopycnals that ventilate the interior Caribbean and subducts along these isopycnals toward the equator as part of the lower limb of the STC (see Figure ) [ Schott et al ., ; Hazeleger and Drijfhout , ].…”

Section: Discussionmentioning

confidence: 99%

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Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

et al. 2015

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We present coral-and sclerosponge-based reconstructions of the 14 C content in North Atlantic dissolved inorganic carbon (DIC) during the last~100 years from the subtropical cells (STCs). These waters are sensitive to the dynamics of the shallow overturning meridional circulation that transports heat and water masses from the subtropics to the tropics. We use these records to investigate the circulation patterns of the off-equatorial upwelling regions of the STCs, which are not well understood. Coral and sclerosponge skeletons provide long time series of ocean DIC 14 C content, a tracer of oceanic circulation, effectively extending the observational record back in time. Sclerosponge data from the Bahamas were used to extend the existing subtropical 14 C time series to the 21st century. Coral 14 C data from the Cape Verde Islands (1890-2002) captured the 14 C signature of water brought to the surface in the off-equatorial regions of the STC present near the West African coast. We observe a unique postbomb trend at Cape Verde that is similar to the upwelling regions in the Pacific, and we interpret this trend as the result of the slow penetration of bomb 14 C into the interior ocean as part of the STC circulation. Using a multibox mixing model we constrain the time history of bomb 14 C in the eastern tropical Atlantic, and we estimate a 20 year time scale for ventilation of the thermocline in this area of the ocean. The similarity between the Atlantic and Pacific 14 C-based records of upwelling suggests that both are caused by bomb 14 C penetration rather than more complex explanations that invoke changes in thermocline depth (e.g., related to El Niño-Southern Oscillation variability) or changes in the strength of the subtropical cells. Our results offer constraints for models of tropical ocean circulation and anthropogenic CO 2 uptake that attempt to reproduce the characteristics of the shallow wind-driven circulation in the Atlantic.

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“…Bermuda data are from Druffel [, ] and Goodkin et al . [], Florida data are from Druffel [], and Puerto Rico data are from Kilbourne et al . [].…”

Section: Resultsmentioning

confidence: 99%

“…Florida data are from Druffel []; Bermuda includes data from Druffel [, ] and Goodkin et al . []. Puerto Rico data are from Kilbourne et al .…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

et al. 2015

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“…Surface Δ 14 C recorded by three Atlantic corals. The records are from the Florida Keys (Druffel & Linick, ; Druffel unpublished), the south coast of Puerto Rico (Kilbourne et al, ), and the south coast of Bermuda (Druffel, ; Goodkin et al, ).…”

Section: Anthropogenic Perturbationsmentioning

confidence: 99%

Upwelling in the Ocean Basins North of the ACC: 1. On the Upwelling Exposed by the Surface Distribution of Δ¹⁴C

et al. 2019

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The upwelling associated with the ocean's overturning circulation is hard to observe directly. Here, a large data set of surface Δ14C measurements is compiled in order to show where deep water is brought back up to the surface in the ocean basins north of the Antarctic Circumpolar Current (ACC). Maps constructed from the data set show that low‐Δ14C deep water from the ACC is drawn up to the surface in or near the upwelling zones off Northwest Africa and Namibia in the Atlantic, off Costa Rica and Peru in the Pacific, and in the northern Arabian Sea in the Indian Ocean. Deep water also seems to be reaching the surface in the subarctic Pacific gyre near the Kamchatka Peninsula. The low‐Δ14C water drawn up to the surface in the upwelling zones is also shown to spread across the ocean basins. It is easily seen, for example, in the western Atlantic off Florida and in the western Pacific off New Guinea and Palau. The spreading allows one to estimate the volumes of upwelling, which, it turns out, are similar to the volumes of large‐scale upwelling derived from inverse box models. This means that very large volumes of cool subsurface water are reaching the surface in and near the upwelling zones—much larger volumes than would be expected from the local winds.

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“…Instead, large scale convective mixing may be driving interannual metal variability in the JSB record. Though thermocline mixing was not evident in a record of radiocarbon variability from the JSB coral (Goodkin et al, 2012), seasonal overturning and convective mixing, when the mixed-layer depth (MLD) reaches 160-200 m, can cause the nutricline to breach and entrain nutrients into the euphotic zone in the western Sargasso Sea (e.g., Copin-Montégut and Avril, 1993;Hansell and Carlson, 2001;Michaels and Knap, 1996). The effects of deep mixing during the winter are reflected in elevated nitrate concentrations in the surface layer (Goericke and Welschmeyer, 1998).…”

Section: John Smith's Baymentioning

confidence: 99%

Environmental assessment of metal exposure to corals living in Castle Harbour, Bermuda

et al. 2013

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Environmental contamination in Castle Harbour, Bermuda, has been linked to the dissolution and leaching of contaminants from the adjacent marine landfill. This study expands the evidence for environmental impact of leachate from the landfill by quantitatively demonstrating elevated metal uptake over the last 30 years in corals growing in Castle Harbour. Coral Pb/Ca, Zn/Ca and Mn/Ca ratios and total Hg concentrations are elevated relative to an adjacent control site in John Smith's Bay. The temporal variability in the Castle Harbour coral records suggests that while the landfill has increased in size over the last 35 years, the dominant input of metals is through periodic leaching of contaminants from the municipal landfill and surrounding sediment. Elevated contaminants in the surrounding sediment suggest that resuspension is an important transport medium for transferring heavy metals to corals. Increased winds, particularly during the 1990s, were accompanied by higher coral metal composition at Castle Harbour. Coupled with wind-induced resuspension, interannual changes in sea level within the Harbour can lead to increased bioavailability of sediment-bound metals and subsequent coral metal assimilation. At John Smith's Bay, large scale convective mixing may be driving interannual metal variability in the coral record rather than impacts from land-based activities. Results from this study provide important insights into the coupling of natural variability and anthropogenic input of contaminants to the nearshore environment.Published by Elsevier B.V.

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Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

Cited by 14 publications

References 30 publications

Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

Upwelling in the Ocean Basins North of the ACC: 1. On the Upwelling Exposed by the Surface Distribution of Δ¹⁴C

Environmental assessment of metal exposure to corals living in Castle Harbour, Bermuda

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Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

Cited by 14 publications

References 30 publications

Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

Upwelling in the Ocean Basins North of the ACC: 1. On the Upwelling Exposed by the Surface Distribution of Δ14C

Environmental assessment of metal exposure to corals living in Castle Harbour, Bermuda

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Upwelling in the Ocean Basins North of the ACC: 1. On the Upwelling Exposed by the Surface Distribution of Δ¹⁴C