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Model-derived uncertainties in deep ocean temperature trends between 1990 and 2010

Model-derived uncertainties in deep ocean temperature trends between 1990 and 2010
Model-derived uncertainties in deep ocean temperature trends between 1990 and 2010

We construct a novel framework to investigate the uncertainties and biases associated with estimates of deep ocean temperature change from hydrographic sections and demonstrate this framework in an eddy-permitting ocean model. Biases in estimates from observations arise due to sparse spatial coverage (few sections in a basin), low frequency of occupations (typically 5–10 years apart), mismatches between the time period of interest and span of occupations, and from seasonal biases relating to the practicalities of sampling during certain times of year. Between the years 1990 and 2010, the modeled global abyssal ocean biases are small, although regionally some biases (expressed as a heat flux into the 4,000- to 6,000-m layer) can be up to 0.05 W/m 2 . In this model, biases in the heat flux into the deep 2,000- to 4,000-m layer, due to either temporal or spatial sampling uncertainties, are typically much larger and can be over 0.1 W/m 2 across an ocean. Overall, 82% of the warming trend deeper than 2,000 m is captured by hydrographic section-style sampling in the model. At 2,000 m, only half the model global warming trend is obtained from observational-style sampling, with large biases in the Atlantic, Southern, and Indian Oceans. Biases due to different sources of uncertainty can have opposing signs and differ in relative importance both regionally and with depth, revealing the importance of reducing temporal and spatial uncertainties in future deep ocean observing design.

decadal variability, deep oceans, observational uncertainties, ocean heat content, ocean modeling, temperature trends
2169-9275
1155-1169
Garry, F. K.
5810f34e-1069-4efb-ba9e-ec13e1f3441d
McDonagh, E. L.
47e26eeb-b774-4068-af07-31847e42b977
Blaker, A. T.
94efe8b2-c744-4e90-87d7-db19ffa41200
Roberts, C. D.
b7b453e7-fc86-4b6a-8878-9a2a67f28e34
Desbruyères, D. G.
93b8e6a5-f026-41f7-8d7e-b10d0dc166fc
Frajka-Williams, E.
da86044e-0f68-4cc9-8f60-7fdbc4dc19cb
King, B. A.
960f44b4-cc9c-4f77-b3c8-775530ac0061
Garry, F. K.
5810f34e-1069-4efb-ba9e-ec13e1f3441d
McDonagh, E. L.
47e26eeb-b774-4068-af07-31847e42b977
Blaker, A. T.
94efe8b2-c744-4e90-87d7-db19ffa41200
Roberts, C. D.
b7b453e7-fc86-4b6a-8878-9a2a67f28e34
Desbruyères, D. G.
93b8e6a5-f026-41f7-8d7e-b10d0dc166fc
Frajka-Williams, E.
da86044e-0f68-4cc9-8f60-7fdbc4dc19cb
King, B. A.
960f44b4-cc9c-4f77-b3c8-775530ac0061

Garry, F. K., McDonagh, E. L., Blaker, A. T., Roberts, C. D., Desbruyères, D. G., Frajka-Williams, E. and King, B. A. (2019) Model-derived uncertainties in deep ocean temperature trends between 1990 and 2010. Journal of Geophysical Research: Oceans, 124 (2), 1155-1169. (doi:10.1029/2018JC014225).

Record type: Article

Abstract

We construct a novel framework to investigate the uncertainties and biases associated with estimates of deep ocean temperature change from hydrographic sections and demonstrate this framework in an eddy-permitting ocean model. Biases in estimates from observations arise due to sparse spatial coverage (few sections in a basin), low frequency of occupations (typically 5–10 years apart), mismatches between the time period of interest and span of occupations, and from seasonal biases relating to the practicalities of sampling during certain times of year. Between the years 1990 and 2010, the modeled global abyssal ocean biases are small, although regionally some biases (expressed as a heat flux into the 4,000- to 6,000-m layer) can be up to 0.05 W/m 2 . In this model, biases in the heat flux into the deep 2,000- to 4,000-m layer, due to either temporal or spatial sampling uncertainties, are typically much larger and can be over 0.1 W/m 2 across an ocean. Overall, 82% of the warming trend deeper than 2,000 m is captured by hydrographic section-style sampling in the model. At 2,000 m, only half the model global warming trend is obtained from observational-style sampling, with large biases in the Atlantic, Southern, and Indian Oceans. Biases due to different sources of uncertainty can have opposing signs and differ in relative importance both regionally and with depth, revealing the importance of reducing temporal and spatial uncertainties in future deep ocean observing design.

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Garry_et_al-2019-Journal_of_Geophysical_Research__Oceans - Version of Record
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More information

Accepted/In Press date: 11 January 2019
e-pub ahead of print date: 28 January 2019
Published date: 1 February 2019
Keywords: decadal variability, deep oceans, observational uncertainties, ocean heat content, ocean modeling, temperature trends

Identifiers

Local EPrints ID: 430377
URI: http://eprints.soton.ac.uk/id/eprint/430377
ISSN: 2169-9275
PURE UUID: 48376b1f-fd1f-434e-8333-f362e8ee22cd
ORCID for F. K. Garry: ORCID iD orcid.org/0000-0002-9640-6675
ORCID for E. Frajka-Williams: ORCID iD orcid.org/0000-0001-8773-7838

Catalogue record

Date deposited: 26 Apr 2019 16:30
Last modified: 07 Oct 2020 06:44

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