Dataset Information

Global ocean synoptic thermocline gradient, isothermal-layer depth, and other upper ocean parameters.

ABSTRACT: Different from the existing global ocean climatological datasets of isothermal layer (ITL) depth (h), a global ocean synoptic dataset of h along with other parameters has been established from temperature profiles of the National Centers for Environmental Information (NCEI) world ocean database 1961-2017. The exponential leap-forward gradient method was used to identify h and thermocline gradient (G) from each temperature profile measured by expendable bathythermograph (XBT) and conductivity, temperature, depth (CTD) instruments. Due to quality and vertical resolution of the profiling data, the numbers of (G, h) pairs are 446,811 out of 964,942 CTD profiles and 755,086 out of 2,303,433 XBT profiles. With the given h, other parameters such as ITL heat content (HITL), sea surface temperature (SST), temperature below ITL (Tm), and quality measures (Q, I) indices are provided. Altogether, the dataset contains 1,201,897 temporally and horizontally varying sets of (G, h, HITL, SST, Tm, Q-index, I-index). Note that we added 200° to the longitude. This synoptic dataset is located on the NCEI website for public use.

SUBMITTER: Chu PC

PROVIDER: S-EPMC6620299 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Global ocean synoptic thermocline gradient, isothermal-layer depth, and other upper ocean parameters.

Chu Peter C PC Fan Chenwu C

Scientific data 20190710 1

Different from the existing global ocean climatological datasets of isothermal layer (ITL) depth (h), a global ocean synoptic dataset of h along with other parameters has been established from temperature profiles of the National Centers for Environmental Information (NCEI) world ocean database 1961-2017. The exponential leap-forward gradient method was used to identify h and thermocline gradient (G) from each temperature profile measured by expendable bathythermograph (XBT) and conductivity, te ...[more]

PMID: 31292448

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Project description:The surface mixed layer of the world ocean regulates global climate by controlling heat and carbon exchange between the atmosphere and the oceanic interior1-3. The mixed layer also shapes marine ecosystems by hosting most of the ocean's primary production4 and providing the conduit for oxygenation of deep oceanic layers. Despite these important climatic and life-supporting roles, possible changes in the mixed layer during an era of global climate change remain uncertain. Here we use oceanographic observations to show that from 1970 to 2018 the density contrast across the base of the mixed layer increased and that the mixed layer itself became deeper. Using a physically based definition of upper-ocean stability that follows different dynamical regimes across the global ocean, we find that the summertime density contrast increased by 8.9 ± 2.7 per cent per decade (10-6-10-5 per second squared per decade, depending on region), more than six times greater than previous estimates. Whereas prior work has suggested that a thinner mixed layer should accompany a more stratified upper ocean5-7, we find instead that the summertime mixed layer deepened by 2.9 ± 0.5 per cent per decade, or several metres per decade (typically 5-10 metres per decade, depending on region). A detailed mechanistic interpretation is challenging, but the concurrent stratification and deepening of the mixed layer are related to an increase in stability associated with surface warming and high-latitude surface freshening8,9, accompanied by a wind-driven intensification of upper-ocean turbulence10,11. Our findings are based on a complex dataset with incomplete coverage of a vast area. Although our results are robust within a wide range of sensitivity analyses, important uncertainties remain, such as those related to sparse coverage in the early years of the 1970-2018 period. Nonetheless, our work calls for reconsideration of the drivers of ongoing shifts in marine primary production, and reveals stark changes in the world's upper ocean over the past five decades.

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Dataset Information

Global ocean synoptic thermocline gradient, isothermal-layer depth, and other upper ocean parameters.

Publications

Global ocean synoptic thermocline gradient, isothermal-layer depth, and other upper ocean parameters.

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