Turbulent Mixing Under Drifting Pack Ice in the Weddell Sea

McPhee, Miles G.; Martinson, Douglas G.

doi:10.1126/science.263.5144.218

Cited by 84 publications

(52 citation statements)

References 24 publications

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“…In the autumn Weddell Sea, Antarctica, K b can be estimated to be $0.6 Â 10 À4 m s À1 from observation at the ice bottom [McPhee and Martinson, 1994]. The value in our case (K b = 1.2 Â 10 À4 m s…”

Section: à3mentioning

confidence: 67%

Sea‐ice melting processes inferred from ice–upper ocean relationships in the Ross Sea, Antarctica

Nihashi¹

2005

J. Geophys. Res.

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[1] Sea-ice melting processes are inferred from various summer sea-ice and upper ocean data obtained in the Ross Sea in January 1999. Using spatially (30 km) averaged continuous data, an ice concentration-water temperature plot (CT-plot) shows that the temperature at a depth of $7 m increases as ice concentration decreases in the ice interior region. The CT-plot is explained by a simple ice-upper ocean coupled model in which sea-ice melting is caused only by heat input through open water. The bulk heat transfer coefficient between ice and ocean (K b ) is estimated to be 1.2 Â 10 À4 m s À1 . These findings are supported by the relationship between ice concentration and heat content in the mixed layer estimated from conductivity-temperature-depth (CTD) data. Salinity at a depth of $7 m, salt deficit in the mixed layer associated with sea-ice melt estimated from CTD data, and their relationships with ice concentration also suggest that melting is mainly caused by atmospheric heat input through open water and that local balance of salinity nearly hold. The time evolution of ice concentration calculated from the ice-upper ocean coupled model with the estimated K b corresponds with that derived from the Special Sensor Microwave Imager (SSM/I), confirming the model's applicability and the value of K b .

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Section: à3mentioning

confidence: 67%

Sea‐ice melting processes inferred from ice–upper ocean relationships in the Ross Sea, Antarctica

Nihashi¹

2005

J. Geophys. Res.

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“…57 ) and mapped from an original horizontal resolution of 25 km onto the horizontal Cartesian grid (1/4°) of the ocean current data prior to use in the advection model. Because sea-ice cover prevents the estimation of altimetry-derived ocean currents, under-ice ocean currents were estimated from the sea-ice motion data, scaling the magnitude of the velocity components by 0.43 and applying an offset of − 35° to the sea-ice motion direction 58,59 . This simplified, fixed relationship gives an indication of the main direction of flow beneath the ice at the regional scale that we are interested in for this study.…”

Section: Statistical Analyses Of Dive Operationsmentioning

confidence: 99%

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

et al. 2017

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A ntarctic krill Euphausia superba, a key species in Southern Ocean food webs 1 , plays a central role in ecosystem processes and community dynamics of apex predators, and is the target of a commercial fishery 2 . Krill spawn in late spring and their larvae develop during summer, autumn and under the ice in winter to emerge as juveniles in the following spring. The newly spawned eggs sink from the surface to up to 1,000 m depth where they hatch and the developing larvae actively swim upwards to feed in the upper water column 1 . Larval Antarctic krill have low lipid reserves, which are insufficient to support long periods of starvation. Therefore, winter, when primary production is minimal, is assumed to be a critical bottleneck for larval krill development and hence recruitment to the adult population 3,4 . Present hypotheses suggest that high algal biomass in winter sea ice enhances larval krill winter-feeding conditions and growth [5][6][7][8] . This implies that larvae have access to this high algal biomass within the sea ice. However, recent observations 9,10 indicate that the linkage between sea ice and krill recruitment success is not as direct as has been suggested. The timing of ice-edge advance and annual ice-season duration is highly variable, and does not necessarily show a clear link to krill recruitment in the following year ( Supplementary Figs. 1 and 2). Along the Antarctic Peninsula, adult krill have a five to six year population cycle with oscillations in biomass exceeding an order of magnitude 9 . According to bioenergetics models, part of the variability is due to interannual variation in reproductive output 11 as well as autumn blooms that may govern the possible overwinter survival rate of larvae 11,12 . In the Bransfield Strait, three krill winter surveys have shown that krill abundance is an order of magnitude higher than in summer, regardless of concurrent sea-ice conditions 10 A dominant Antarctic ecological paradigm suggests that winter sea ice is generally the main feeding ground for krill larvae. Observations from our winter cruise to the southwest Atlantic sector of the Southern Ocean contradict this view and present the first evidence that the pack-ice zone is a food-poor habitat for larval development. In contrast, the more open marginal ice zone provides a more favourable food environment for high larval krill growth rates. We found that complex under-ice habitats are, however, vital for larval krill when water column productivity is limited by light, by providing structures that offer protection from predators and to collect organic material released from the ice. The larvae feed on this sparse ice-associated food during the day. After sunset, they migrate into the water below the ice (upper 20 m) and drift away from the ice areas where they have previously fed. Model analyses indicate that this behaviour increases both food uptake in a patchy food environment and the likelihood of overwinter transport to areas where feeding conditions are more favourable in spring.

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“…McPhee and Martinson (1994) show that the turbulent energy peak found in the vertical velocity spectrum scaled by the wavenumber (kS ww (k)) can be used to find the peak mixing length (λ) in the ocean boundary layer by max 0.85 ,…”

Section: Evolution Of Turbulent Eddies Through the Nstm Layermentioning

confidence: 99%

Field observations and results of a 1-D boundary layer model for developing near-surface temperature maxima in the Western Arctic

Gallaher

Stanton

Shaw

et al. 2017

Elementa: Science of the Anthropocene

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Gallaher, SG et al 2017 Field observations and results of a 1-D boundary layer model for developing near-surface temperature maxima in the Western Arctic. Elem Sci Anth, 5: 11, pp. 1-21, DOI: https://doi.org/10.1525/elementa.195 IntroductionRecent changes in the Arctic ice-ocean system have led to an increase in upper ocean heating. The primary source of this heating is the two-fold rise in ocean-absorbed solar radiation (Perovich et al., 2007) that results from rapidly declining summer sea ice extent (Comiso et al., 2008;Steele et al., 2010). Recent studies in the Canada Basin show that this absorbed solar heating is partitioned 0.23/0.77 between ocean heat storage and latent heat loss (basal ice melt), respectively (Toole et al., 2010;Gallaher et al., 2016). Most of the oceanic heat is accumulated in near-surface temperature maximum (NSTM) features. The NSTM is defined as an upper ocean (< 50 m) temperature maximum that: 1) is at least 0.2°C above freezing (δT); 2) has a salinity < 31; and 3) resides above a cooler water layer by at least 0.1°C (Jackson et al., 2010). Jackson et al. (2010) attribute NSTM development to the absorption of solar radiation in shallow, stratified layers beneath melting sea ice and open water during summer. Steele et al. (2011) present an additional formation process caused by cooling of the near-surface ocean under open water areas in late summer, which leaves behind a warmer subsurface layer. Although NSTM heat is gained in the summer, the release of this heat often occurs in later seasons. Observations in the Canada Basin show that the NSTM often survives into fall, and that heat from this layer can be mixed into the surface mixed layer to delay or slow freeze up (Steele et al., 2008;Jackson et al., 2010;Steele et al., 2011;Timmermans, 2015).Early studies of the NSTM during AIDJEX (Maykut and McPhee, 1995) and SHEBA (McPhee et al., 1998) found that the layer was present directly below the summer surface mixed layer, at depths between 25 and 35 m. However, the Canada Basin upper ocean is freshening (McPhee et al., 2009) Summer sea ice extent in the Western Arctic has decreased significantly in recent years resulting in increased solar input into the upper ocean. Here, a comprehensive set of in situ shipboard, on-ice, and autonomous ice-ocean measurements were made of the early stages of formation of the near-surface temperature maximum (NSTM) in the Canada Basin. These observations along with the results from a 1-D turbulent boundary layer model indicate that heat storage associated with NSTM formation is largely due to the absorption of penetrating solar radiation just below a protective summer halocline. The depth of the summer halocline was found to be the most important factor for determining the amount of solar radiation absorbed in the NSTM layer, while halocline strength controlled the amount of heat removed from the NSTM by turbulent transport. Observations using the Naval Postgraduate School Turbulence Frame show that the NSTM was able to persist despite periods of i...

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Turbulent Mixing Under Drifting Pack Ice in the Weddell Sea

Cited by 84 publications

References 24 publications

Sea‐ice melting processes inferred from ice–upper ocean relationships in the Ross Sea, Antarctica

Sea‐ice melting processes inferred from ice–upper ocean relationships in the Ross Sea, Antarctica

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

Field observations and results of a 1-D boundary layer model for developing near-surface temperature maxima in the Western Arctic

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