Multiyear Sea Ice Research Articles

A millennial‐scale record of Arctic Ocean sea ice variability and the demise of the Ellesmere Island ice shelves

Sea‐ice ice shelves, at the apex of North America (>80° N), constitute the oldest sea ice in the Northern Hemisphere. We document the establishment and subsequent stability of the Ward Hunt Ice Shelf, and multiyear landfast sea ice in adjacent fiords, using 69 radiocarbon dates obtained on Holocene driftwood deposited prior to coastal blockage. These dates (47 of which are new) record a hiatus in driftwood deposition beginning ∼5500 cal yr BP, marking the inception of widespread multiyear landfast sea ice across northern Ellesmere Island. This chronology, together with historical observations of ice shelf breakup (∼1950 to present), provides the only millennial‐scale record of Arctic Ocean sea ice variability to which the past three decades of satellite surveillance can be compared. Removal of the remaining ice shelves would be unprecedented in the last 5500 years. This highlights the impact of ongoing 20th and 21st century climate warming that continues to break up the remaining ice shelves and soon may cause historically ice‐filled fiords nearby to open seasonally.

Changing sea ice melt parameters in the Canadian Arctic Archipelago: Implications for the future presence of multiyear ice

Estimates of annual sea ice melt onset, freeze onset, and melt duration are made within the Canadian Arctic Archipelago (CAA) using SeaWinds/QuikSCAT data from 2000 to 2007. The average date of melt onset occurred on day 150, the average freeze onset occurred on day 266, and the average number of days of melt was 116. Melt onset occurred first, and freeze onset occurred last within the Amundsen, Western Arctic Waterway, and Eastern Parry Channel regions, whereas the reverse occurred in the Queen Elizabeth Islands (QEI) and the M'Clure and Viscount‐Melville regions. Multiyear sea ice (MYI) increases occurred from 2000 to 2004 because of dynamic import and first‐year sea ice (FYI) being promoted to MYI, but this replenishment virtually stopped from 2005 to 2007, coincident with longer melt seasons. Only after two consecutive long melt seasons (2005–2006) and almost no replenishment were regions to the south of the QEI cleared of MYI. We argue that this is because MYI must slowly ablate on the underside while in transit within the CAA from the small oceanic heat flux and can therefore survive for several years in southern regions without replenishment. Net positive dynamic MYI import into the CAA was observed in 2007 following MYI removal during 2005–2006. Longer melt seasons will continue to reduce the inventory of FYI in the CAA following the melt season. Longer melt seasons within the CAA will likely not reduce MYI dynamic import, but it remains to be seen whether or not this MYI will be able to survive longer melt seasons as it migrates to the southern regions.

New evidence from the western Canadian Arctic Archipelago for the resubmergence of Bering Strait

Widespread molluscan samples were collected from raised marine sediments to date the last retreat of the NW Laurentide Ice Sheet from the western Canadian Arctic Archipelago. At the head of Mercy Bay, northern Banks Island, deglacial mud at the modern coast contains Hiatella arctica and Portlandia arctica bivalves, as well as Cyrtodaria kurriana, previously unreported for this area. Multiple H. arctica and C. kurriana valves from this site yield a mean age of 11.5 14C ka BP (with 740 yr marine reservoir correction). The occurrence of C. kurriana, a low Arctic taxon, raises questions concerning its origin, because evidence is currently lacking for a molluscan refugium in the Arctic Ocean during the last glacial maximum. Elsewhere, the oldest late glacial age available on C. kurriana comes from the Laptev Sea where it is < 10.3 14C ka BP and attributed to a North Atlantic source. This is 2000 cal yr younger than the Mercy Bay samples reported here, making the Laptev Sea, ~ 3000 km to the west, an unlikely source. An alternate route from the North Atlantic into the Canadian Arctic Archipelago was precluded by coalescent Laurentide, Innuitian and Greenland ice east of Banks Island until ~ 10 14C ka BP. We conclude that the presence of C. kurriana on northern Banks Island records migration from the North Pacific. This requires the resubmergence of Bering Strait by 11.5 14C ka BP, extending previous age determinations on the reconnection of the Pacific and Arctic oceans by up to 1000 yr. This renewed ingress of Pacific water likely played an important role in re-establishing Arctic Ocean surface currents, including the evacuation of thick multi-year sea ice into the North Atlantic prior to the Younger Dryas geochron.

Denitrification activity and oxygen dynamics in Arctic sea ice

Denitrification and oxygen dynamics were investigated in the sea ice of Franklin Bay (70°N), Canada. These investigations were complemented with measurements of denitrification rates in sea ice from different parts of the Arctic (69°N–85°N). Potential for bacterial denitrification activity (5–194 μmol N m−2 day−1) and anammox activity (3–5 μmol N m−2 day−1) in melt water from both first-year and multi-year sea ice was found. These values correspond to 27 and 7%, respectively, of the benthic denitrification and anammox activities in Arctic sediments. Although we report only potential denitrification and anammox rates, we present several indications that active denitrification in sea ice may occur in Franklin Bay (and elsewhere): (1) despite sea ice-algal primary production in the lower sea ice layers, heterotrophic activity resulted in net oxygen consumption in the sea ice of 1–3 μmol l−1 sea ice per day at in situ light conditions, suggesting that O2 depletion may occur prior to the spring bloom. (2) The ample organic carbon (DOC) and NO3 − present in sea ice may support an active denitrification population. (3) Measurements of O2 conditions in melted sea ice cores showed very low bulk concentrations, and in some cases anoxic conditions prevailed. (4) Laboratory studies using planar optodes for measuring the high-resolution two-dimensional O2 distributions in sea ice confirmed the very dynamic and heterogeneous O2 distribution in sea ice, displaying a mosaic of microsites of high and low O2 concentrations. Brine enclosures and channels were strongly O2 depleted in actively melting sea ice, and anoxic conditions in parts of the brine system would favour anaerobic processes.

Late glacial to Holocene climatic and oceanographic record of sediment facies from the South Scotia Sea off the northern Antarctic Peninsula

Two gravity cores were collected from the South Scotia Sea located off the northern Antarctic Peninsula during the 2002/2003 Korea Antarctic Research Program (KARP) expedition to determine the late Quaternary climatic and oceanographic history. Reassessment of previous sedimentological, geochemical and micropaleontological analyses combined with established age model of AMS 14C dates represent the reliable record of late Pleistocene climatic/oceanographic change for the Scotia Sea region of Antarctica. During the Last Glacial Maximum (LGM), the South Scotia Sea received large amounts of sorted terrigenous sediments and some of the reworked diatom fossils emplaced by bottom currents from an extensively glaciated Weddell Sea continental margin. Drifting icebergs calved from the glacial fronts have dispersed glacial dropstones throughout the study area. The bottom current deposits during the glacial phase comprise two lithologic units: (1) bioturbated gravelly sandy mud (Facies 1), formed by sluggish bottom current caused by reduced dense-water production originated from the ice sheet on the Weddell Shelf, (2) indistinctly layered diatomaceous mud as shown by total organic carbon (TOC) highs in the Facies 1, deposited by sporadic bottom currents caused by intensified sea–ice formation in polynya during the glacial stage. The LGM is characterized by greater and longer sea–ice coverage and a restricted Weddell/Scotia summer communication, as evidenced by a relative decrease in percentage Thalssiosira antarctica and Chaetoceros resting spores, which are more abundant close to the Weddell Ice Shelf. Deglaciation (about 13,000–9000 14C yr BP) in the South Scotia Sea was characterized by increasing TOC, diatom abundance, and decreasing magnetic susceptibility and sand contents up core. At this time, subglacial meltwater streams began to emanate from the Weddell Ice Sheet with peak of ice rafting. Sediment-laden turbid plumes from melting glacier and deglaciated Weddell Shelf have probably been joined into the realm of contour currents, Weddell Gyre circulation, ultimately forming indistinctly laminated gravelly mud (Facies 2) in the South Scotia Sea. These currents probably resulted from water exchange between the Weddell Ice Shelf and Circumpolar Warm Deep Water during the retreating phase of the last glaciation. The deglaciation was probably followed by a period of open-marine conditions with variable extent of sea ice (variable TOC content). Between about 9000 and 3000 14C yr BP, bottom water production occasionally appears to have diminished or ceased due to the disintegration of some of the Weddell Ice Shelf, and biogenic input became increased forming bioturbated diatomaceous mud and ooze (Facies 3). The climatic amelioration could have restored the Weddell/Scotia communication during the summer, as evidenced by a relative increase of T. antarctica and C. resting spore in Facies 3. At the onset of Neoglacial (about 3000 14C yr BP), a decrease in TOC and diatom abundance, and an increase of sand content reflect the formation of more extensive and seasonally persistent multiyear sea ice. The Weddell Ice Shelf advanced with increased sea–ice coverage at this time, and as a result, bottom water might play a role in transporting terrigenous sediments and reworked fossil diatoms into the South Scotia Sea, forming diatomaceous sandy mud (Facies 4). During this time, it is possible that the Weddell/Scotia communication would have been partly restricted, as evidenced by a reduction of the numbers of T. antarctica and C. resting spores. Our results indicate environmental variability throughout the late Quaternary that was consistent across most portions of the maritime Antarctic Peninsula. In addition, the timing of climatic transitions correlates with the Northern Hemisphere, indicating the possibility of coherent climatic variability during the late Quaternary, at least for the higher latitudes.

The occurrence of Eualus gaimardii gibba Krøyer 1841 (Crustacea, Decapoda) in the sympagic habitat: an example of bentho-sympagic coupling

We report the first records of a decapod species (Eualus gaimardii gibba) in association with Arctic multiyear sea-ice. Seven specimens inhabiting brine channels in the ice were collected during two field campaigns (September 2003, March/April 2004) by diver operated suction samplers. Salinity tolerance experiments (14–50 PSU) suggest that the species is stenohaline. Gut examinations revealed remains of the sympagic amphipod Gammarus wilkitzkii. All collected individuals were found in ice above relatively shallow waters (60–100 m depth) suggesting bentho-sympagic coupling.

Structure, salinity and isotopic composition of multi-year landfast sea ice in Nella Fjord, Antarctica

The structural, salinity and stable oxygen-isotopic properties of multi-year landfast sea-ice samples collected from Nella Fjord, East Antarctica were used to determine the ice formation process and the fractional contribution of snow, in both snow ice and superimposed ice, to the total sea-ice thickness. The textural analysis of the sea-ice cores revealed a general structure of a granular surface layer, horizontal c-axis in the columnar ice and, in some cases, a “buried” granular-ice layer at depth between two columnar-ice layers. The textural and isotopic properties of the ice core samples indicate that thermodynamic mechanisms alone are responsible for the development of the multi-year fast ice in the region investigated. Superimposed ice contributed 5% to the ice thickness at some sites. Using a mid-range isotopic criterion to distinguish between snow ice and frazil ice in the granular layers, we estimate that snow-ice layers contributed 38% of the total ice thickness in the samples. The actual fraction of snow in the granular-ice layers in different cores was from 1% to 24% of the total sea-ice thickness.

Near zero replenishment of the Arctic multiyear sea ice cover at the end of 2005 summer

The remarkably low Arctic multiyear (MY) sea ice coverage following the summer of 2005 is placed in the context of its variability over the past seven years (2000–2006). Annual cycles of MY ice coverage, from QuikSCAT and satellite passive ice motion, show that the replenishment of MY ice area at the end of this summer is near zero (0.1 × 106 km2) compared to the previous five summers of 1.0, 1.2, 0.4, 0.4, and 0.9 × 106 km2. This is examined in terms of anomalies in ice export and the record of freezing (FDD) and melting degree‐days (MDD). The 2005 summer (Jun–Sep) saw the highest Fram Strait ice export (&gt;0.25 × 106 km2) compared to the 7‐year mean of 0.14 × 106 km2. This directly explains ∼40% of the decrease in MY coverage of 0.6 × 106 km2 between Jan 2005 and Jan 2006. The cumulative effects of the recent warmer winters and summers, relative to the longer‐term record since 1958, explain the balance. For this short record, the combination of spatially averaged FDD and MDD anomalies of the preceding year explain ∼63% of the variance in the replenishment areas.

Direct measurement of sea ice thermal conductivity: No surface reduction

We present new laboratory measurements of the thermal conductivity of small cores of landfast first‐year (FY) and multiyear (MY) sea ice from McMurdo Sound, Antarctica. The conductivity of surface (0–10 cm) and subsurface (45–55 cm) FY ice, 2.14 ± 0.11 and 2.09 ± 0.11 W m–1 K–1, respectively, and MY surface ice, 1.88 ± 0.13 W m–1 K–1, are all consistent with effective medium predictions for measured salinity, density, and temperature. In contrast with a previous result from thermistor array measurements in FY ice, the present measurements in FY ice show no conductivity reduction over the top 50 cm. We have reexamined the analysis of these previous array measurements and have identified analytical effects that rendered this analysis unreliable in the presence of high‐frequency surface temperature variations and pronounced surface warming and cooling events. We conclude that this apparent near‐surface conductivity reduction was an artefact.

Modeling the summertime evolution of sea‐ice melt ponds

We present a mathematical model describing the summer melting of sea ice. We simulate the evolution of melt ponds and determine area coverage and total surface ablation. The model predictions are tested for sensitivity to the melt rate of unponded ice, enhanced melt rate beneath the melt ponds, vertical seepage, and horizontal permeability. The model is initialized with surface topographies derived from laser altimetry corresponding to first‐year sea ice and multiyear sea ice. We predict that there are large differences in the depth of melt ponds and the area of coverage between the two types of ice. We also find that the vertical seepage rate and the melt rate of unponded ice are important in determining the total surface ablation and area covered by melt ponds.

Spectral transmission and implications for the partitioning of shortwave radiation in arctic sea ice

AbstractWe present a new set of values for the spectral extinction coefficients,Kλ, for the interior of first-year (FY) and multi-year (MY) Arctic sea ice during the summer melt season measured during SHEBA (Surface Heat Budget of the Arctic Ocean program) and at Barrow, Alaska, USA. Results for FY ice are consistent with previously reported values, and differences can be understood in terms of variations in the concentration of biological and suspended particulate material. The values for the interior of MY ice are lower than previously reported for both bare and ponded ice. For bare MY ice the newKλvalues predict a substantial increase in the solar radiation transmitted through the ice into the upper mixed layer. Ponded MY ice is only slightly more transparent than previously reported, and FY ice values are generally consistent with previously reported values. Assuming an asymmetry parameter of 0.94, the extinction coefficients are consistent with a volume-scattering coefficient of 77 m–1that is constant from 400 to at least 720 nm.

Unexpectedly high radioactivity burdens in ice-rafted sediments from the Canadian Arctic Archipelago

Unexpectedly high specific activities of 137Cs (1800–2000 Bq kg − 1 dry weight) have been detected in fine-grained sediments entrained in multi-year sea ice floes grounded in Resolute Bay near the center of the Northwest Passage through the Canadian Arctic Archipelago. These results are remarkable because: (1) the specific activities are about two orders of magnitude higher than average specific activities detected in previous studies of sea ice rafted sediments from the Arctic Ocean, (2) two independent observations of these unexpectedly high specific activities were made several years apart, (3) the sampling site is on the opposite side of the Arctic basin from potential radioactive sources such as disposal and weapons testing sites of the former Soviet Union and nuclear fuel reprocessing sites in western Europe, and (4) the closest compositional match to known geologic source regions is Banks Island, on the western edge of the Arctic Archipelago, although a smaller number of grains from one of the two samples were mineralogically matched to sediments in the Laptev Sea. Consequently, the sediments are probably not from a single distinct source and were likely mixed during sea ice transport. Coupled with previous observations of higher radionuclide specific activities in some sea ice rafted sediments relative to bottom sediments, these new observations indicate that comparatively high as well as variable radioactive contaminant burdens in ice rafted sediments must be common and geographically independent of proximity to known contaminant sources. The mechanisms that would facilitate these unexpected high radionuclide burdens in sea ice are not known and require additional study, as well as investigations of the implications for the transport and fate of contaminants in Arctic sea ice.

On the sensitivity of undeformed Arctic sea ice to its vertical salinity profile

The temporal evolution of sea ice salinity affects the temperature profile and vertical growth and decay of the ice cover, as well as many other important properties. Here, we use a one‐dimensional thermodynamic sea ice model to explore the sensitivity to the vertical profile of ice salinity of (1) Arctic first‐year and equilibrium multiyear sea ice thickness, and (2) the salt/freshwater flux at the ice/ocean interface. Results indicate that increasing the mean salinity induces a higher thermal inertia reducing summer melt and finally increasing ice thickness. The shape of the profile is also important, since low salinity at the surface must be captured to produce enough surface melt. This study gives accurate hints on what the minimum complexity of a parameterization of the temporal evolution of sea ice salinity should be.

Possible effect of boreal wildfire soot on Arctic sea ice and Alaska glaciers

Abstract The role of black carbon (BC) soot in the Arctic as an agent of climate warming through forcing/feedback of sea ice/glacier albedo is an uncertainty in need of addressing. In-situ measurements of BC-aerosols and gas byproducts from the FROSTFIRE experiment burn, 8–11 July 1999, are used with a coupled high-resolution wind field/empirical fall-out model to assess transport/dispersion and estimate deposition. Results suggest that BC-aerosols (soot) are quickly transported from central Alaska to the Arctic Ocean region of multi-year sea ice and to southern Alaska glaciers, where up to 20% can be deposited. The estimate of BC soot concentration from Alaska boreal wildfires favorably compares to in-situ sea ice observations made in 1998 and snow albedo observation on Gulkana Glacier in 2001. We hypothesize that northern boreal wildfires are a possible contributor in the reduction of first/multi-year sea ice/glacier extent by enhancing summer melting from albedo reduction. Should the occurrence and severity of northern boreal wildfires continue as in summer 2004, during which more than 670 km 2 burned and was the worst wildfire year on record, there will be implications for Northern hemisphere climate warming.

Variations in the Arctic's multiyear sea ice cover: A neural network analysis of SMMR-SSM/I data, 1979–2004

[1] A 26-year (1979–2004) observational record of January multiyear sea ice distributions, derived from neural network analysis of SMMR-SSM/I passive microwave satellite data, reveals dense and persistent cover in the central Arctic basin surrounded by expansive regions of highly fluctuating interannual cover. Following a decade of quasi equilibrium, precipitous declines in multiyear ice area commenced in 1989 when the Arctic Oscillation shifted to a pronounced positive phase. Although extensive survival of first-year ice during autumn 1996 fully replenished the area of multiyear ice, a subsequent and accelerated decline returned the depletion to record lows. The most dramatic multiyear sea ice declines occurred in the East Siberian, Chukchi, and Beaufort Seas.

Comparison of sea ice signatures in OKEAN and RADARSAT radar images for the northeastern Barents Sea

Sea ice signatures in near-simultaneous OKEAN real aperture radar (RAR) and RADARSAT synthetic aperture radar (ScanSAR) images have been analyzed and compared for the northeastern part of the Barents Sea in April 1998. Signatures of major sea ice types and features in these images have been identified and verified by in situ observations on board the nuclear icebreaker Sovetsky Soyuz. It is shown that both RAR and ScanSAR images can be used for detection of new, young, first year, and multiyear sea ice types, multiyear and fast ice boundaries, flaw polynyas, wide fractures, giant and vast ice floes, and large areas of rough ice. Backscatter signatures of the major sea ice types are analyzed and compared, and the backscattering differences between the ice types are estimated for both types of data. High-resolution ScanSAR images are found to be particularly suited for discrimination of narrow leads and level areas in compact sea ice. A study of the radar signatures of a flaw polynya to the north of Cape Zhelaniya was conducted using ERS SAR, RADARSAT ScanSAR, and OKEAN RAR over a period of 33 h. The backscatter from the polynya varied significantly between VV and HH polarization and as a consequence of changing physical properties due to freezing during the 33 h period. Access to satellite radar data for use in sea ice research will increase in the near future. Wide-swath SAR data are available from both RADARSAT and ENVISAT from 2003, and a new RAR satellite, SICH-M1, is planned for launch in 2004.

Annual cycles of multiyear sea ice coverage of the Arctic Ocean: 1999–2003

For the years 1999–2003, we estimate the time‐varying perennial ice zone (PIZ) coverage and construct the annual cycles of multiyear (MY, including second year) ice coverage of the Arctic Ocean using QuikSCAT backscatter, MY fractions from RADARSAT, and the record of ice export from satellite passive microwave observations. An area balance approach extends the winter MY coverage from QuikSCAT to the remainder of the year. From these estimates, the coverage of MY ice at the beginning of each year is 3774 × 103 km2 (2000), 3896 × 103 km2 (2001), 4475 × 103 km2 (2002), and 4122 × 103 km2 (2003). Uncertainties in coverage are ∼150 × 103 km2. In the mean, on 1 January, MY ice covers ∼60% of the Arctic Ocean. Ice export reduces this coverage to ∼55% by 1 May. From the multiple annual cycles, the area of first‐year (FY) ice that survives the intervening summers are 1192 × 103 km2 (2000), 1509 × 103 km2 (2001), and 582 × 103 km2 (2002). In order for the MY coverage to remain constant from year to year, these replenishment areas must balance the overall area export and melt during the summer. The effect of the record minimum in Arctic sea ice area during the summer of 2002 is seen in the lowest area of surviving FY ice of the three summers. In addition to the spatial coverage, the location of the PIZ is important. One consequence of the unusual location of the PIZ at the end of the summer of 2002 is the preconditioning for enhanced export of MY ice into the Barents and Kara seas. Differences between the minimums in summer sea ice coverage from our estimates and passive microwave observations are discussed.

Spatial and temporal multiyear sea ice distributions in the Arctic: A neural network analysis of SSM/I data, 1988–2001

Arctic multiyear sea ice concentration maps for January 1988–2001 were generated from SSM/I brightness temperatures (19H, 19V, and 37V) using modified multiple layer perceptron neural networks. Learning data for the neural networks were extracted from ice maps derived from Okean and ERS satellite imagery to capitalize on the stability of active radar multiyear ice signatures. Evaluations of three learning algorithms and several topologies indicated that networks constructed with error back propagation learning and 3‐20‐1 topology produced the most consistent and physically plausible results. Operational neural networks were developed specifically with January learning data, and then used to estimate daily multiyear ice concentrations from daily‐averaged SSM/I brightness temperatures during January. Monthly mean maps were produced for analysis by averaging the respective daily estimates. The 14‐year series of January multiyear ice distributions revealed dense and persistent cover in the central Arctic surrounded by expansive regions of highly fluctuating interannual cover. Estimates of total multiyear ice area by the neural network were intermediate to those of other passive microwave algorithms, but annual fluctuations and trends were similar among all algorithms. When compared to Radarsat estimates of multiyear ice concentration in the Beaufort and Chukchi Seas (1997–1999), average discrepancies were small (0.9–2.5%) and spatial coherency was reasonable, indicating the neural network's Okean and ERS learning data facilitated passive microwave inversion that emulated backscatter signatures. During 1988–2001, total January multiyear ice area declined at a significant linear rate of −54.3 × 103 km2 yr−1 (−1.4% yr−1). The most persistent and extensive decline in multiyear ice concentration (−3.3% yr−1) occurred in the southern Beaufort and Chukchi Seas. In autumn 1996, a large multiyear ice recruitment of over 106 km2 (mostly in the Siberian Arctic) fully replenished the previous 8‐year decline in total area, but it was followed by an accelerated and compensatory decline during the subsequent 4 years. Seventy‐five percent of the interannual variation in January multiyear sea ice area was explained by linear regression on two atmospheric parameters: the previous winter's (JFM) Arctic Oscillation index as a proxy to melt duration and the previous year's average sea level pressure gradient across the Fram Strait as a proxy to annual ice export. Consecutive year changes (1994–2001) in January multiyear ice volume were significantly correlated with duration of the intervening melt season (R2 = 0.73, −80.0 km3 d−1), emphasizing a large thermodynamic influence on the Arctic's mass sea ice balance during summers with anomalous melt durations.

Abundance and composition of the sea-ice meiofauna in off-shore pack ice of the Beaufort Gyre in summer 2002 and 2003

We studied the abundance, biomass and potential ingestion rates of meiofauna in multi-year sea ice (MYI) of the Beaufort Gyre during two icebreaker expeditions in summers 2002 and 2003. Ice cores were taken at a total of ten stations and analyzed for ice temperature, salinity, chlorophyll a (Chl a), and ice meiofauna abundances. In 2002, ice was free of snow and covered with melt ponds. In 2003, snow still covered the ice and a slush-layer was found in the ice-water interface. The vertical distribution of Chl a mostly followed C-shaped curves with elevated concentrations at the bottom and top of the ice. Ice meiofauna was mainly restricted to the bottom 10 cm of the ice and was dominated by turbellarians, harpacticoid copepods and nematodes. The meiofauna abundances (range: 8–3,000 individuals m−2) and Chl a concentration (range: 0.1–1.7 mg Chl a m−2) were similar to estimates for MYI of the Transpolar Drift, but about 2 orders of magnitude below coastal fast first-year ice estimates. Calculated potential meiofaunal ingestion rate, based on allometric equations and volume estimates from the literature, was about 1% of published daily algal production rates and was thus unlikely to constrain algal biomass accumulation.

Hydraulic controls of summer Arctic pack ice albedo

Linkages between albedo, surface morphology, melt pond distribution, and properties of first‐year and multiyear sea ice have been studied at two field sites in the North American Arctic between 1998 and 2001. It is shown that summer sea‐ice albedo depends critically on surface melt‐pond hydrology, controlled by melt rate, ice permeability, and topography. Remarkable short‐term and interannual variability in pond fraction varying by more than a factor of 2 and hence area‐averaged albedo (varying between 0.28 and 0.49 over the period of a few days) were observed to be forced by millimeter to centimeter changes in pond water level. Tracer studies show that the depth of the snow cover, by controlling the amount of superimposed ice formation in early summer, critically affects the retention of meltwater at the ice surface and hence affects pond coverage. Ice roughness as determined by deformation and aging processes explains a significant portion of the contrasts in pond coverage and albedo between ice of different ages, suggesting that a reduction in multiyear ice area and sea‐ice residence time in the Arctic Ocean is accompanied by large‐scale ice albedo decreases. Our work indicates that ice‐albedo prediction in large‐scale models with conventional methods is inherently difficult, if not impossible. However, a hydrological model, incorporating measured statistics of ice topography, reproduces observed pond features and variability, pointing toward an alternative approach in predicting ice albedo in numerical simulations.