Subsurface melting of a free-floating Antarctic iceberg

Stephenson, Gordon; Sprintall, Janet; Gille, Sarah T.; Vernet, María; Helly, J.; Kaufmann, Ronald S.

doi:10.1016/j.dsr2.2010.11.009

Cited by 54 publications

(72 citation statements)

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“…Physical properties of icebergs and their surrounding waters Icebergs included in this study were studied in waters of the northwestern Weddell Sea, characterized by Antarctic Surface Water and Winter Water (Stephenson et al 2011), and in waters of the Scotia Sea. In situ surface water temperatures varied from -0.94 to 0.54°C and salinities of 33.698-34.148 in fall and from -1.60 to 0.00°C and salinities of 33.946-34.713 in winter.…”

Section: Resultsmentioning

confidence: 99%

Diatoms (Bacillariophyceae) associated with free-drifting Antarctic icebergs: taxonomy and distribution

2015

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Free-drifting Antarctic icebergs can alter the phytoplankton in surrounding waters. In addition, diatom mats live attached to the submerged walls of the icebergs. In this study we describe a diverse diatom community associated with these mats and an atypical planktonic community in waters affected by icebergs. Samples were collected in the winter of 2008 and fall of 2009 from Antarctic icebergs and their adjacent waters, utilizing a remote operated vehicle and plankton nets, respectively, and subsequently analyzed using light and electron microscopy. Thalassioneis signyensis, dominant species growing on the icebergs' flanks, provided substrate for other diatoms, mainly Synedropsis lata var. angustata, Synedropsis recta, Fragilaria cf. islandica var. adeliae, Attheya gaussii, Navicula cf. perminuta, Amphora sp. and Nitzschia spp. New morphological characteristics are given for S. lata var. angustata, S. recta and A. gaussii. We report also Biddulphia alternans and Coscinodiscus concinnus for the first time in Antarctic waters. Similar to sea ice algae, the term sympagic is used to describe the habitat of these diatom communities. A particular planktonic community is also found close to icebergs, including diatoms known to have a benthic, epiphytic, sympagic or freshwater habitat: Amphora sp., B. alternans, Cocconeis spp., Delphineis minutissima, Licmophora gracilis, Luticola cf. australomutica, Opephora sp., Pinnularia spp., Plagiogramma sp., Psammodictyon panduriforme var. minor, Pseudogomphonema kamtschaticum, Rhaphoneis amphiceros, S. recta and T. signyensis. Our results support the hypothesis that species associated with icebergs exchange freely with plankton, ice shelves and sea ice, suggesting that icebergs can act as physical agents to transport and distribute organisms in between these habitats.

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Section: Resultsmentioning

confidence: 99%

Diatoms (Bacillariophyceae) associated with free-drifting Antarctic icebergs: taxonomy and distribution

2015

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“…The Weddell Sea (Figure 1) has distinct water masses that are characterized by their temperature and salinity [Weiss, 1979;Jacobs and Fairbanks, 1984;Garabato et al, 2002;Stephenson et al, 2011]. Those of interest in this study are, in order from the surface to depth: Antarctic surface water (AASW), winter water (WW), Warm Deep Water (WDW), which is a type of circumpolar deep water (CDW) [Garabato et al, 2002], and Weddell Sea Deep Water (WSDW).…”

Section: Water Massesmentioning

confidence: 99%

“…A few of these samples were collected from the surface using a towfish [Lin et al, 2011] but most were collected by Niskin bottles at discrete depths. Of 65 CTD casts performed during the cruise, 56 were deeper than 250 m, with most of these profiles going deeper than 500 to 600 m [Stephenson et al, 2011]. Samples (80 mL) were sealed and transported back to the Scripps Institution of Oceanography, stored at ambient temperature, and subsequently sent to the USGS Reston Stable Isotope Laboratory for isotopic analysis.…”

Section: Water Massesmentioning

confidence: 99%

“…These two sources, meteoric water from a calved piece of C18A ice and WDW, are used as end-members in the estimation of meteoric water fraction in section 2.1. mapping of the Control site as well as the location of the sample sites: C18A, Away, Control, and Iceberg Alley (IA). The sampling methodology is described in Helly et al [2011a] and Stephenson et al [2011].…”

Section: Water Massesmentioning

confidence: 99%

“…This standing mass of icebergs is comparable in magnitude (10 15 210 16 kg) [Silva et al, 2006;Tournadre et al, 2012] to the maximum mass of seasonal sea ice that sur- [Helly et al, 2011a[Helly et al, , 2011b and hydrocasts through the pycnocline [Stephenson et al, 2011] have been used to describe the Near-field and Far-field spatial and temporal distributions of salinity and temperature in relation to a large free-drifting iceberg.…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of the meltwater field from a large Antarctic iceberg using

et al. 2015

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Large tabular icebergs represent a disruptive influence on a stable water column when drifting in the open ocean. This is a study of one iceberg, C18A, encountered in the Powell Basin in the Weddell Sea in March 2009, formed from iceberg C18 ( 76×7 km) originating from the Ross Ice Shelf in May 2002. C18A was lunate in shape with longest dimensions of 31 km×7 km×184 m. The meltwater field from C18A was characterized using δ18O from water samples collected near C18A (Near‐field, 0.4–2 km) and contrasted with a Far‐field comprised of samples from an Away site (19 km from C18A), a Control site (70 km away), and a region populated with small icebergs (Iceberg Alley, 175 km away). The in‐sample fractions of meteoric water were calculated relative δ18O in iceberg ice and Weddell Deep Water and converted to meteoric water height (m) and a percentage within 100 m depth bins. The Near‐field and Far‐field difference from surface to 200 m was 0.51±0.28%. The concentration of meteoric water dropped to approximately half that value below 200 m, approximate keel depth of the iceberg, although detectable to 600 m. From surface to 600 m, the overall difference was statistically significant ( P<0.0001). From this, we estimate the Near‐field volume astern of the iceberg ( 0.16 km3normald−1) as a continuous source of meteoric water.

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Observations indicative of rain‐induced double diffusion in the ocean surface boundary layer

Walesby

Vialard

Minnett

et al. 2015

Geophysical Research Letters

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Double diffusion can result in the formation of thermohaline staircases, typically observed in the ocean interior. The observations presented here were acquired in the ocean surface boundary layer with the autonomous microstructure Air‐Sea Interaction Profiler. An intense rain event (rainfall rates of up to 35 mm/h) resulted in cooler, fresher water (up to 0.15 practical salinity unit (psu) over the upper 7–10 m) overlaying warmer, saltier water, a situation potentially conducive to double‐diffusive mixing. Although not as crisp as interfaces in the interior ocean because of elevated background mixing, a total of 303 thermohaline interfaces were detected within and at the base of the fresh layer, with mean changes in temperature (T) and salinity (S) across interfaces of 20 × 10−3∘C and 22 × 10−3 psu, respectively. These results call for new studies to disambiguate whether such interfaces are formed through double‐diffusive mixing or shear instabilities and understand any long‐term impacts on near‐surface stratification.

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Subsurface melting of a free-floating Antarctic iceberg

Cited by 54 publications

References 25 publications

Diatoms (Bacillariophyceae) associated with free-drifting Antarctic icebergs: taxonomy and distribution

Diatoms (Bacillariophyceae) associated with free-drifting Antarctic icebergs: taxonomy and distribution

Characteristics of the meltwater field from a large Antarctic iceberg using

Observations indicative of rain‐induced double diffusion in the ocean surface boundary layer

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