Middepth decadal warming and freshening in the South Atlantic

Giglio, Donata; Johnson, Gregory C.

doi:10.1002/2016jc012246

Cited by 14 publications

(22 citation statements)

References 33 publications

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“…However, the present estimate is based on more recent data that are more widely distributed around the basin, making it less susceptible to biases owing to sparse coverage issues (Figure 1), and reducing formal uncertainties slightly. The increasing warming with decreasing pressure, exhibiting substantial, statistically significant values at 2,000 dbar, is also consistent with other analyses of middepth warming in the region using both repeat hydrographic section and core Argo profile data (Giglio & Johnson, 2017).…”

Section: Discussionsupporting

confidence: 89%

Antarctic Bottom Water Warming in the Brazil Basin: 1990s Through 2020, From WOCE to Deep Argo

Johnson

Cadot

Lyman

et al. 2020

Geophysical Research Letters

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A warming trend of 2.1 (±0.4) m°C yr −1 in bottom waters (4,500 to 5,900 dbar) spreading north from Antarctica through the Brazil Basin is quantified by comparing 2019-2020 data from a new Deep Argo regional pilot array to 1989-1995 data from full-depth zonal and meridional hydrographic sections occupied across the basin before and during the World Ocean Circulation Experiment (WOCE). Additionally, float temperatures are about 0.046°C warmer than those from a long-term climatology in those same bottom waters. Lower North Atlantic Deep Water in the basin shows no detectable warming, but Upper North Atlantic Deep Water exhibits evidence of warming in both analyses. The bottom-intensified warming results in a reduction in vertical density stratification between the bottom and deep waters of about 1% per decade. This change is in contrast with the effects of surface-intensified warming, which tends to increase vertical density stratification. Plain Language Summary Surface waters around Antarctica become very cold, salty, and dense through atmosphere and ice exchanges. After cascading down the continental shelf to the abyssal ocean, they spread northward as "Antarctic Bottom Waters." Widespread warming of these waters over the past few decades has been detected by analyses of data from decadal occupations of a set of worldwide, transoceanic research cruises. The better to monitor and understand these and other deep ocean changes, international oceanographers are working together to deploy arrays of oceanic robots (Deep Argo floats) that collect oceanographic data from the sea surface to its floor and report them in real time. We analyze data from one of these arrays, recently deployed in the Brazil Basin. By comparing the Deep Argo data collected from 2019 to 2020 with data collected from 1989-1995 during research cruises in the region, we quantify the warming trend of Antarctic Bottom Water as 0.002°C yr −1 over that time period, which is about one seventh the global sea surface temperature warming trend from 1989-2019. Furthermore, since the bottom waters are warming, but the deep waters above them are not, the density difference between them is lessening over the decades, potentially influencing ocean mixing and circulation.

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Section: Discussionsupporting

confidence: 89%

Antarctic Bottom Water Warming in the Brazil Basin: 1990s Through 2020, From WOCE to Deep Argo

Johnson

Cadot

Lyman

et al. 2020

Geophysical Research Letters

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“…This long-term trend agrees with warming observed during the last decade, when profiling floats greatly improved spatial sampling (e.g., Giglio and Johnson, 2017). The water masses north and within the Antarctic Circumpolar Current have warmed at a rate of 0.1°-0.2°C per decade in the upper 1 km (Figures 1 and 4).…”

Section: Observed Temperature Trendssupporting

confidence: 82%

“…Comparing temperature measurements obtained at the end of the twentieth century or early in the twenty-first century with temperature records of previous decades is unambiguous: the Southern Ocean within and north of the Antarctic Circumpolar Current has warmed at all depths Llovel and Terray (2016) in the upper 2,000 m at a more rapid rate than the globally averaged ocean warming (Figure 4a,b; Gille, 2008 ;Böning et al, 2008;Giglio and Johnson, 2017). This long-term trend agrees with warming observed during the last decade, when profiling floats greatly improved spatial sampling (e.g., Giglio and Johnson, 2017).…”

Section: Observed Temperature Trendsmentioning

confidence: 76%

Southern Ocean Warming

Sallée¹,

Cnrs²

2018

Oceanog

106

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“…The heat taken up in the subpolar seas is then transported northward and accumulate within and north of the Antarctic Circumpolar Current, in the first 1 km of the water column which is well ventilated (Mode and Intermediate Waters; Figure 8). Strong warming at a rate of ∼0.2 • C/decade is observed in this region of the Southern Ocean (Böning et al, 2008;Gille, 2008;Giglio and Johnson, 2017). Similarly, the freshening trend observed in the subpolar seas, propagates with the northward and downward circulation, within the Antarctic Circumpolar Current, in the AAIWs ventilated in the first 1 km of the water column (Figure 8; Durack and Wijffels, 2010).…”

Section: Case Study: Southern Oceanmentioning

confidence: 63%

Adequacy of the Ocean Observation System for Quantifying Regional Heat and Freshwater Storage and Change

et al. 2019

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Considerable advances in the global ocean observing system over the last two decades offers an opportunity to provide more quantitative information on changes in heat and freshwater storage. Variations in these storage terms can arise through internal variability and also the response of the ocean to anthropogenic climate change. Disentangling these competing influences on the regional patterns of change and elucidating their governing processes remains an outstanding scientific challenge. This challenge is compounded by instrumental and sampling uncertainties. The combined use of ocean observations and model simulations is the most viable method to assess the forced signal from noise and ascertain the primary drivers of variability and change. Moreover, this approach offers the potential for improved seasonal-to-decadal predictions and the possibility to develop powerful multi-variate constraints on climate model future projections. Regional heat storage changes dominate the steric contribution to sea level rise over most of the ocean and are vital to understanding both global and regional heat budgets. Variations in regional freshwater storage are particularly relevant to our understanding of changes in the hydrological cycle and can potentially be used to verify local ocean mass addition from terrestrial and cryospheric systems associated with contemporary sea level rise. This White Paper will examine the ability of the current ocean observing system to quantify changes in regional heat and freshwater storage. In particular we will seek to answer the question: What time and space scales are currently Frontiers in Marine Science | www.frontiersin.org 1 August 2019 | Volume 6 | Article 416Palmer et al.Regional Heat and Freshwater Observations resolved in different regions of the global oceans? In light of some of the key scientific questions, we will discuss the requirements for measurement accuracy, sampling, and coverage as well as the synergies that can be leveraged by more comprehensively analyzing the multi-variable arrays provided by the integrated observing system.

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Middepth decadal warming and freshening in the South Atlantic

Cited by 14 publications

References 33 publications

Antarctic Bottom Water Warming in the Brazil Basin: 1990s Through 2020, From WOCE to Deep Argo

Antarctic Bottom Water Warming in the Brazil Basin: 1990s Through 2020, From WOCE to Deep Argo

Southern Ocean Warming

Adequacy of the Ocean Observation System for Quantifying Regional Heat and Freshwater Storage and Change

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