Decadal variation of isopycnal layer in the Indian Ocean based on WOA18 dataset

doi:10.3969/j.issn.1001-909X.2020.04.003

Abstract

Abstract: The climatology distribution of isopycnal layer in the Indian Ocean were analyzed based on the WOA18 (World Ocean Atlas 2018) dataset firstly. And then three time periods were defined as 1985-1994, 1995-2004 and 2005-2017 to research the decadal variation. The results show the climatology distributions of 11 isopycnal layers. As far as σ₀=26.00kg/m³ (reference pressure as 0 dbar) isopycnal layer was concerned, the layer was outcropping at roughly 40°S. As the potential density increased, the outcrop area of the isopycnal layer gradually moved southward until it disappeared. When the potential density was greater than σ₀=26.95 kg/m³ and less than or equal to σ₂=37.00kg/m³, the deepest part of the isopycnal layers were located in southern Madagascar, and the depth of the North Indian Ocean was almost the same. Furthermore, present study investigates the decadal variances of depth and salinity of isopycnal layers, where the three layers include σ₀=26.00 kg/m³, σ₁=31.87 kg/m³ (reference pressure as 1 000 dbar) and σ₂=36.805kg/m³ (reference pressure as 2 000 dbar). Studies show that the depth and salinity of the isopycnal layer had significant decadal changes in the three periods from 1985 to 2017. For the isopycnal layer of σ₀=26.00kg/m³, the depth decreased first and then increased during the three periods. And the decadal variation of the isopycnal depth was mainly located in 30°S-40°S(the rapid change area of the isopycnal depth). The difference of salinity between 1995-2004 and 1985-1994 was basically opposite to the difference between 2005-2017 and 1995-2004 when the isopycnal layer was σ₀=26.00kg/m³. For the isopycnal layer of σ₁=31.87kg/m³ and σ₂=36.805kg/m³, the decadal variations of the depth were concentrated on 40°S-50°S. Overall, the salinity of σ₁=31.87kg/m³ show a decreasing trend but σ₂=36.805kg/m³ show an increase trend.

Key words: the Indian Ocean, isopycnal layer, decadal variance

CLC Number:

P731.1
P724

WU Shouchang, HE Hailun, CHEN Meixiang, WANG Yuan, LIN Feilong. Decadal variation of isopycnal layer in the Indian Ocean based on WOA18 dataset[J]. Journal of Marine Sciences, 2020, 38(4): 26-39.

References

[1] CESSI P. The global overturning circulation[J]. Annual Review of Marine Science, 2019, 11(1): 249-270.
[2] SCHOTT F A, XIE Shangping, MCCREARY JR J P. Indian Ocean circulation and climate variability[J]. Reviews of Geophysics, 2009, 47(1): RG1002.
[3] ZIKA J D, ENGLAND M H, SIJP W P. The ocean circulation in thermohaline coordinates[J]. Journal of Physical Oceanography, 2012, 42(5): 708-724.
[4] SCHOTT F A, MCCREARY JR J P. The monsoon circulation of the Indian Ocean[J]. Progress in Oceanography, 2001, 51(1): 1-123.
[5] WANG Weiqiang, KÖHL A, STAMMER D. The deep meridional overturning circulation in the Indian Ocean inferred from the GECCO synthesis[J]. Dynamics of Atmospheres and Oceans, 2012, 58(11): 44-61.
[6] WANG Weiqiang, ZHU Xiuhua, WANG Chunzai, et al. Deep meridional overturning circulation in the Indian Ocean and its relation to Indian Ocean Dipole[J]. Journal of Climate, 2014, 27(12): 4508-4520.
[7] LUYTEN J R, PEDLOSKY J, STOMMEL H. The ventilated thermocline[J]. Journal of Physical Oceanography, 1983, 13(2): 292-309.
[8] BEAL L M, FFIELD A, GORDON A L. Spreading of Red Sea overflow waters in the Indian Ocean[J]. Journal of Geophysical Research: Oceans, 2000, 105(C4): 8549-8564.
[9] REID J L. On the total geostrophic circulation of the Indian Ocean: Flow patterns, tracers, and transports[J]. Progress in Oceanography, 2003, 56(1): 137-186.
[10] MCCREARY JR J P, LU Peng. Interaction between the subtropical and equatorial ocean circulations: The subtropical cell[J]. Journal of Physical Oceanography, 1994, 24(2): 466-497.
[11] NAGURA M, MCPHADEN M J. The shallow overturning circulation in the Indian Ocean[J]. Journal of Physical Oceanography, 2018, 48(2): 413-434.
[12] DURACK P J, WIJFFELS S E. Fifty-year trends in global ocean salinities and their relationship to broad-scale warming[J]. Journal of Climate, 2010, 23(16): 4342-4362.
[13] SOLOMON S, MANNING M, MARQUIS M, et al. Climate change 2007: the physical science basis: Working group I contribution to the fourth assessment report of the IPCC[M]. Cambridge: Cambridge University Press, 2007: 23-30.
[14] GILLE S T. Warming of the Southern Ocean since the 1950s[J]. Science, 2002, 295(5558): 1275-1277.
[15] ALORY G, WIJFFELS S, MEYERS G. Observed temperature trends in the Indian Ocean over 1960-1999 and associated mechanisms[J]. Geophysical Research Letters, 2007, 34(2):L02606.
[16] HAN Weiqing, VIALARD J, MCPHADEN M J, et al. Indian Ocean decadal variability: A review[J]. Bulletin of the American Meteorological Society, 2014, 95(11): 1679-1703.
[17] ZWENG M M, REAGAN J R, SEIDOV D, et al. World ocean atlas 2018, volume 2: Salinity[Z]//MISHONOV A. NOAA Atlas NESDIS 82, 2019: 1-50.
[18] LOCARNINI R A, MISHONOV A V, BARANOVA O K, et al. World ocean atlas 2018, volume 1: Temperature[Z]//MISHONOV A. NOAA Atlas NESDIS 81, 2018.
[19] MCDOUGALL T J, BARKER P M. Getting started with TEOS-10 and the Gibbs Seawater (GSW) oceanographic toolbox[M]. SCOR/IAPSO WG, 2011: 1-28.