Winter mixed layer entrainment of Weddell Deep Water

1984 ◽  
Vol 89 (C1) ◽  
pp. 637 ◽  
Author(s):  
A. L. Gordon ◽  
C. T. A. Chen ◽  
W. G. Metcalf
Keyword(s):  
Mixed Layer ◽  
Deep Water ◽  
Winter Mixed Layer

scholarly journals Diagnosing Natural Variability of North Atlantic Water Masses in HadCM3

2005 ◽  
Vol 18 (12) ◽  
pp. 1925-1941 ◽  
Author(s):  
Keith Haines ◽  
Chris Old
Keyword(s):  
Mixed Layer ◽  
General Circulation ◽  
Circulation Model ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Mode Water ◽  
Surface Heat Fluxes ◽  
Mode Waters ◽  
Winter Mixed Layer

Abstract A study of thermally driven water mass transformations over 100 yr in the ocean component of the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) is presented. The processes of surface-forced transformations, subduction and mixing, both above and below the winter mixed layer base, are quantified. Subtropical Mode Waters are formed by surface heat fluxes and subducted at more or less the same rate. However, Labrador Seawater and Nordic Seawater classes (the other main subduction classes) are primarily formed by mixing within the mixed layer with very little formation directly from surface heat fluxes. The Subpolar Mode Water classes are dominated by net obduction of water back into the mixed layer from below. Subtropical Mode Water (18°C) variability shows a cycle of formation by surface fluxes, subduction ∼2 yr later, followed by mixing with warmer waters below the winter mixed layer base during the next 3 yr, and finally obduction back into the mixed layer at 21°C, ∼5 yr after the original formation. Surface transformation of Subpolar Mode Waters, ∼12°C, are led by surface transformations of warmer waters by up to 5 yr as water is transferred from the subtropical gyre. They are also led by obduction variability from below the mixed layer, by ∼2 yr. The variability of obduction in Subpolar Mode Waters also appears to be preceded, by 3–5 yr, by variability in subduction of Labrador Sea Waters at ∼6°C. This supports a mechanism in which southward-propagating Labrador seawater anomalies below the subpolar gyre can influence the upper water circulation and obduction into the mixed layer.

scholarly journals Silicon pool dynamics and biogenic silica export in the Southern Ocean inferred from Si-isotopes

Ocean Science ◽  
2011 ◽  
Vol 7 (5) ◽  
pp. 533-547 ◽  
Author(s):  
F. Fripiat ◽  
A.-J. Cavagna ◽  
F. Dehairs ◽  
S. Speich ◽  
L. André ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Silicic Acid ◽  
Mixed Layer ◽  
Deep Water ◽  
Biogenic Silica ◽  
Polar Front ◽  
Intermediate Water ◽  
Subtropical Zone ◽  
Isotopic Signatures ◽  
The Antarctic

Abstract. Silicon isotopic signatures (δ30Si) of water column silicic acid (Si(OH)4) were measured in the Southern Ocean, along a meridional transect from South Africa (Subtropical Zone) down to 57° S (northern Weddell Gyre). This provides the first reported data of a summer transect across the whole Antarctic Circumpolar Current (ACC). δ30Si variations are large in the upper 1000 m, reflecting the effect of the silica pump superimposed upon meridional water transfer across the ACC: the transport of Antarctic surface waters northward by a net Ekman drift and their convergence and mixing with warmer upper-ocean Si-depleted waters to the north. Using Si isotopic signatures, we determine different mixing interfaces: the Antarctic Surface Water (AASW), the Antarctic Intermediate Water (AAIW), and thermoclines in the low latitude areas. The residual silicic acid concentrations of end-members control the δ30Si alteration of the mixing products and with the exception of AASW, all mixing interfaces have a highly Si-depleted mixed layer end-member. These processes deplete the silicic acid AASW concentration northward, across the different interfaces, without significantly changing the AASW δ30Si composition. By comparing our new results with a previous study in the Australian sector we show that during the circumpolar transport of the ACC eastward, the δ30Si composition of the silicic acid pools is getting slightly, but significantly lighter from the Atlantic to the Australian sectors. This results either from the dissolution of biogenic silica in the deeper layers and/or from an isopycnal mixing with the deep water masses in the different oceanic basins: North Atlantic Deep Water in the Atlantic, and Indian Ocean deep water in the Indo-Australian sector. This isotopic trend is further transmitted to the subsurface waters, representing mixing interfaces between the surface and deeper layers. Through the use of δ30Si constraints, net biogenic silica production (representative of annual export), at the Greenwich Meridian is estimated to be 5.2 ± 1.3 and 1.1 ± 0.3 mol Si m−2 for the Antarctic Zone and Polar Front Zone, respectively. This is in good agreement with previous estimations. Furthermore, summertime Si-supply into the mixed layer of both zones, via vertical mixing, is estimated to be 1.6 ± 0.4 and 0.1 ± 0.5 mol Si m−2, respectively.

Temporal variations of the winter mixed layer south of the Kuroshio Extension

2010 ◽  
Vol 66 (1) ◽  
pp. 147-153 ◽  
Author(s):  
Hikaru Iwamaru ◽  
Fumiaki Kobashi ◽  
Naoto Iwasaka
Keyword(s):  
Mixed Layer ◽  
Kuroshio Extension ◽  
Temporal Variations ◽  
Winter Mixed Layer ◽  
The Kuroshio

scholarly journals Subduction over the Southern Indian Ocean in a High-Resolution Atmosphere–Ocean Coupled Model

2011 ◽  
Vol 24 (15) ◽  
pp. 3830-3849 ◽  
Author(s):  
Mei-Man Lee ◽  
A. J. George Nurser ◽  
I. Stevens ◽  
Jean-Baptiste Sallée
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Current System ◽  
Mixed Layer Depth ◽  
Coupled Model ◽  
Horizontal Resolution ◽  
Layer Depth ◽  
Mode Water ◽  
Coarse Resolution ◽  
Winter Mixed Layer

Abstract This study examines the subduction of the Subantarctic Mode Water in the Indian Ocean in an ocean–atmosphere coupled model in which the ocean component is eddy permitting. The purpose is to assess how sensitive the simulated mode water is to the horizontal resolution in the ocean by comparing with a coarse-resolution ocean coupled model. Subduction of water mass is principally set by the depth of the winter mixed layer. It is found that the path of the Agulhas Current system in the model with an eddy-permitting ocean is different from that with a coarse-resolution ocean. This results in a greater surface heat loss over the Agulhas Return Current and a deeper winter mixed layer downstream in the eddy-permitting ocean coupled model. The winter mixed layer depth in the eddy-permitting ocean compares well to the observations, whereas the winter mixed layer depth in the coarse-resolution ocean coupled model is too shallow and has the wrong spatial structure. To quantify the impacts of different winter mixed depths on the subduction, a way to diagnose local subduction is proposed that includes eddy subduction. It shows that the subduction in the eddy-permitting model is closer to the observations in terms of the magnitudes and the locations. Eddies in the eddy-permitting ocean are found to 1) increase stratification and thus oppose the densification by northward Ekman flow and 2) increase subduction locally. These effects of eddies are not well reproduced by the eddy parameterization in the coarse-resolution ocean coupled model.

scholarly journals The North Pacific Climatology of Winter Mixed Layer and Mode Waters

2004 ◽  
Vol 34 (1) ◽  
pp. 3-22 ◽  
Author(s):  
Toshio Suga ◽  
Kazunori Motoki ◽  
Yoshikazu Aoki ◽  
Alison M. Macdonald
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Mode Waters ◽  
The North ◽  
Winter Mixed Layer ◽  
The North Pacific

Formation and Subduction of Central Mode Water Based on Profiling Float Data, 2003–08

2011 ◽  
Vol 41 (1) ◽  
pp. 113-129 ◽  
Author(s):  
Eitarou Oka ◽  
Shinya Kouketsu ◽  
Katsuya Toyama ◽  
Kazuyuki Uehara ◽  
Taiyo Kobayashi ◽  
...  
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Large Scale ◽  
Kuroshio Extension ◽  
Subtropical Gyre ◽  
Late Winter ◽  
Mode Water ◽  
Central Mode Water ◽  
Winter Mixed Layer ◽  
Central Mode

Abstract Temperature and salinity data from Argo profiling floats in the North Pacific during 2003–08 have been analyzed to study the structure of winter mixed layer north of the Kuroshio Extension and the subsurface potential vorticity distribution in the subtropical gyre in relation to the formation and subduction of the central mode water (CMW). In late winter, two zonally elongated bands of deep mixed layer extend at 33°–39° and 39°–43°N, from the east coast of Japan to 160°W. These correspond to the formation region of the lighter variety of CMW (L-CMW) and that of the denser variety of CMW (D-CMW) and the recently identified transition region mode water (TRMW), respectively. In the western part of the L-CMW and D-CMW–TRMW formation regions west of 170°E, the winter mixed layer becomes deeper and lighter to the east (i.e., to the downstream). As a result, the formed mode water is reentrained into the mixed layer in the farther east in the following winter and modified to the lighter water and is thus unable to be subducted to the permanent pycnocline. In the eastern part of the formation regions between 170°E and 160°W, on the other hand, the winter mixed layer becomes shallower and lighter to the east. From these areas, the L-CMW with potential density of 25.7–26.2 kg m−3 and the D-CMW–TRMW (mostly the former) of 26.1–26.4 kg m−3 are subducted to the permanent pycnocline, and they are then advected anticyclonically in the subtropical gyre. These results imply that during the analysis period large-scale subduction to the permanent pycnocline occurs in the density range up to 26.4 kg m−3 in the open North Pacific, whereas the winter mixed layer density reaches the maximum of 26.6 kg m−3. This is supported by the vertical distribution of apparent oxygen utilization in a hydrographic section in the subtropical gyre.

scholarly journals Distribution and Modification of North Pacific Intermediate Water around the Subarctic Frontal Zone East of 150°E

2009 ◽  
Vol 39 (6) ◽  
pp. 1462-1474 ◽  
Author(s):  
Masachika Masujima ◽  
Ichiro Yasuda
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
Climatological Data ◽  
Profiling Float ◽  
Low Salinity ◽  
Winter Mixed Layer ◽  
Density Surface ◽  
Area North

Abstract Modification and distribution of North Pacific Intermediate Water (NPIW) in the area north of 30°N and east of 150°E are discussed based on an isopycnal particle tracking experiment with the velocity field estimated from a β-spiral inverse method based on climatological data, annual climatological data analysis, and isopycnal-tracking profiling float data. NPIW emanating from 149.5°E between 35.5° and 37.5°N retains its salinity minimum structure along the eastward flow of the northern subtropical gyre, and these pathways occupy the northern part of the NPIW distribution. On the other hand, NPIW from 149.5°E between 37.5° and 40.5°N loses its salinity minimum as it flows eastward to the “transition domain.” The extinction of the salinity minimum structure is caused by a salinity decrease in the upper layer (26.5–26.6 σθ) in the region at 40°–45°N, 155°–165°E where a winter mixed layer is developed to a depth of 300 m and a density of 26.7 σθ. This extinction was observed by a profiling float tracking a 26.7-σθ isopycnal density surface. Low-salinity subarctic water advected southward across the Subarctic Front by wind-induced Ekman drift from strong westerlies in winter is suggested as the source of the low-salinity mixed layer. After the extinction of the salinity minimum structure, a state without salinity minimum is maintained during transport eastward in the transition domain because the winter mixed layer in the area east of the deep mixed layer region reaches a density surface shallower than 26.5 σθ.

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