Late Ice Retreat Research Articles

Influence of Riverine Discharge and Timing of Ice Retreat on Particle Sedimentation Patterns on the Laptev Sea Shelf

AbstractWe studied the influence of river discharge and timing of ice retreat on sinking fluxes of total particulate matter and its components in the Laptev Sea in August–September 2017 and 2018. Vertical fluxes were measured with short‐term sediment traps located on the shelf adjusted to the Lena and Khatanga Rivers inflows (four shallow stations in 2017) and in Vilkitski Strait/Trough area (two deeper stations) in 2018. One station outside the Khatanga plume was repeated in both years. The effect of river discharge manifested by high total particle flux (1–1.6 g m−2 d−1), high Si (0.3 g m−2 d−1) and Al (0.1 g m−2 d−1) fluxes, a high proportion of terrigenous organic carbon (10.7%–27.5% total organic carbon) was clearly recognizable only in the shelf area closest to the Lena inflow. Large contribution of the lithogenic matter to the flux on the Laptev shelf is suggested to result also from sediment resuspension (caused by the tidal mixing and upwelling events), lateral offshore transport of sediment just above the seabed, and coastal abrasion. The magnitude of vertical fluxes of total particulate matter and organic carbon was two to three times higher in 2017 (late ice retreat) than in 2018 (early ice retreat). Centric diatoms dominated protist flux in 2017 while in 2018, dinoflagellates and tintinnids dominated. The contribution of protists to the biogenic organic carbon flux reached 62% in 2018 versus <1% in 2017. Zooplankton fecal pellet flux was not influenced by river discharge but was higher soon after ice melt.

Development and Calibration of Seasonal Probabilistic Forecasts of Ice-Free Dates and Freeze-Up Dates

AbstractDynamical forecasting systems are being used to skillfully predict deterministic ice-free and freeze-up date events in the Arctic. This paper extends such forecasts to a probabilistic framework and tests two calibration models to correct systematic biases and improve the statistical reliability of the event dates: trend-adjusted quantile mapping (TAQM) and nonhomogeneous censored Gaussian regression (NCGR). TAQM is a probability distribution mapping method that corrects the forecast for climatological biases, whereas NCGR relates the calibrated parametric forecast distribution to the raw ensemble forecast through a regression model framework. For NCGR, the observed event trend and ensemble-mean event date are used to predict the central tendency of the predictive distribution. For modeling forecast uncertainty, we find that the ensemble-mean event date, which is related to forecast lead time, performs better than the ensemble variance itself. Using a multidecadal hindcast record from the Canadian Seasonal to Interannual Prediction System (CanSIPS), TAQM and NCGR are applied to produce categorical forecasts quantifying the probabilities for early, normal, and late ice retreat and advance. While TAQM performs better than adjusting the raw forecast for mean and linear trend bias, NCGR is shown to outperform TAQM in terms of reliability, skill, and an improved tendency for forecast probabilities to be no worse than climatology. Testing various cross-validation setups, we find that NCGR remains useful when shorter hindcast records (~20 years) are available. By applying NCGR to operational forecasts, stakeholders can be more confident in using seasonal forecasts of sea ice event timing for planning purposes.

Variation in annual production of copepods, euphausiids, and juvenile walleye pollock in the southeastern Bering Sea

We synthesize recent research on variation in annual production of copepods (Calanus spp.), euphausiids (Thysanoessa spp.), and juvenile walleye pollock (Gadus chalcogrammus) in the southeastern Bering Sea. We reach five conclusions: 1) the timing of the spring bloom is more important than the amount of annual primary production for the transfer of primary to secondary production (i.e., timing matters); 2) summer and fall, not just spring, matter: organisms must maximize energy intake devoted to somatic growth and storage of lipids and minimize energy expenditures during each season; 3) stored lipids are important for the overwinter survival of both zooplankton and age-0 walleye pollock; 4) variation in ice extent and timing of ice retreat affect the spatial distributions of phytoplankton, zooplankton, and age-0 walleye pollock; when these spatial distributions match in late-ice-retreat years, the annual production of copepods, euphausiids, and juvenile walleye pollock often increases (i.e., location matters); 5) if years with late ice retreat, which favor copepod, euphausiid, and juvenile walleye pollock production, occur in succession, top–down control increases. These conclusions help to explain annual variation in production of copepods, euphausiids and juvenile walleye pollock. Copepods and euphausiids often are more abundant in cold years with late ice retreat than in warm years with early ice retreat due to bloom timing and the availability of ice algae during years with late ice retreat. As a consequence, age-0 walleye pollock consume lipid-enriched prey in cold years, better preparing them for their first winter and their overwinter survival is greater. In addition, there is a spatial match of primary production, zooplankton, and age-0 walleye pollock in cold years and a mismatch in warm years.

Influence of timing of sea ice retreat on phytoplankton size during marginal ice zone bloom period on the Chukchi and Bering shelves

Abstract. The size structure and biomass of a phytoplankton community during the spring bloom period can affect the energy use of higher-trophic-level organisms through the predator–prey body size relationships. The timing of the sea ice retreat (TSR) also plays a crucial role in the seasonally ice-covered marine ecosystem, because it is tightly coupled with the timing of the spring bloom. Thus, it is important to monitor the temporal and spatial distributions of a phytoplankton community size structure. Prior to this study, an ocean colour algorithm was developed to derive phytoplankton size index FL, which is defined as the ratio of chlorophyll a (chl a) derived from cells larger than 5 µm to the total chl a, using satellite remote sensing for the Chukchi and Bering shelves. Using this method, we analysed the pixel-by-pixel relationships between FL during the marginal ice zone (MIZ) bloom period and TSR over the period of 1998–2013. The influences of the TSR on the sea surface temperature (SST) and changes in ocean heat content (ΔOHC) during the MIZ bloom period were also investigated. A significant negative relationship between FL and the TSR was widely found in the shelf region during the MIZ bloom season. However, we found a significant positive (negative) relationship between the SST (ΔOHC) and TSR. Specifically, an earlier sea ice retreat was associated with the dominance of larger phytoplankton during a colder and weakly stratified MIZ bloom season, suggesting that the duration of the nitrate supply, which is important for the growth of large-sized phytoplankton in this region (i.e. diatoms), can change according to the TSR. In addition, under-ice phytoplankton blooms are likely to occur in years with late ice retreat, because sufficient light for phytoplankton growth can pass through the ice and penetrate into the water columns as a result of an increase in solar radiation toward the summer solstice. Moreover, we found that both the length of the ice-free season and the annual median of FL positively correlated with the annual net primary production (APP). Thus, both the phytoplankton community composition and growing season are important for the APP in the study area. Our findings showed a quantitative relationship between the interannual variability of FL, the TSR, and the APP, which suggested that satellite remote sensing of the phytoplankton community size structure is suitable to document the impact of a recent rapid sea ice loss on the ecosystem of the study region.

Abundance and distribution of pacific walrus <i>Odobenus rosmarus divergens</i> in vicinity of Cape Serdtse-Kamen in 2009-2013

Results of the first special research of pacific walrus Odobenus rosmarus divergens at Cape Serdtse-Kamen conducted in the 2009-2011 and 2013 are presented. The coastal haulout place looks as series of relatively isolated areas (up to 36) located alongshore about 20 km from Cape Serdtse-Kamen to the Ikalyurynveem River mouth. Initially the walruses were on the northwestern edge of the haulout place between Cape Serdtse-Kamen and Cape Sulyn but expanded southeastward with increasing of their number. In the years with early and intense ice melting, the walruses come to the area in early September, and the haulout forms to the end of the first 10-day period of this month. In conditions of late ice retreat, as in the 2013, the walruses on the whole come to Cape Serdthse-Kamen later. The maximum number of walruses in this area was observed in 2009 (about 98,000 animals) and 2010 (118,500). This is the record number of walruses ever recorded simultaneously on one coastal haulout in the species range. Almost the whole Pacific population gathers in the vicinity of Cape Serdtse-Kamen for feeding in late autumn and continues to feed there until freezing of the Chukchi Sea. In spite of obvious significance of the area at Cape Serdtse-Kamen for the pacific walrus population, there still aren’t any special measures of their protection in this part of the coast when they are ashore - the measures are definitely necessary to prevent intensive economic activities in this key for the walruses area and to save the coastal haulout for traditional use of native people.

Interannual summer variability in euphausiid populations on the eastern Bering Sea shelf during the recent cooling event (2008–2010)

The recent cooling in the eastern Bering Sea resulted in a series of cold years (2008–2010) marked by extensive ice coverage and late ice retreat. In the present study, we examined the spatial and temporal variability of three predominant euphausiid species Thysanoessa raschii, Thysanoessa inermis, and Thysanoessa longipes in the summers of 2008–2010. Simple box-and-whisker plots as well as generalized additive models (GLMs) were applied to examine habitat selection for three euphausiid species. The coefficients of dispersion were calculated for three species to examine potential changes in spatial patterns. Results showed that T. raschii was broadly distributed in the inner and middle domains. The abundance of T. raschii was related to water temperature, salinity and chlorophyll a concentration. T. inermis was primarily distributed in the middle domain and was related to water temperature and salinity. T. longipes was mostly distributed in the outer domain and was only related to salinity. The proportion of T. raschii, a coastal species in the inner and middle domains, showed large interannual variation with the highest in 2008 and the lowest in 2009 (a >50% decline). This same species did not show large interannual variation in the spatial distribution. T. longipes, a shelf species in the outer domain, did not show large interannual variation in abundance, but the center of mass distribution consistently shifted northward and offshore from 2008 to 2010. T. inermis, a coastal species in the middle and coastal domains, did not show large interannual variation in abundance and spatial distribution. In summary, euphausiid populations showed large spatial and temporal variability among cold years. Different species could be affected by different processes in the southeastern Bering Sea.

Emergence of the Arctic Themisto libellula (Amphipoda: Hyperiidae) on the southeastern Bering Sea shelf as a result of the recent cooling, and its potential impact on the pelagic food web

AbstractPinchuk, A. I., Coyle, K. O., Farley, E. V., and Renner, H. M. 2013. Emergence of the Arctic Themisto libellula (Amphipoda: Hyperiidae) on the southeastern Bering Sea shelf as a result of the recent cooling, and its potential impact on the pelagic food web. – ICES Journal of Marine Science, 70: 1244–1254. The eastern Bering Sea shelf experienced a sequence of warm years after a regime shift in the late 1970s. Following a series of unusually warm years in the early 2000s, the climate shifted again in 2007 to a series of extremely cold years that were marked by intense ice coverage and late ice retreat. Spatial and temporal variability in zooplankton communities during the recent cold period was investigated as part of the collaborative BEST-BSIERP program. An increasing presence of the Arctic hyperiid Themisto libellula, which had not been reported from the southeastern Bering Sea since the 1970s, was observed in the Middle Shelf Domain, indicating a developing structural shift in the zooplankton community in response to continuous cold conditions. Simultaneously, T. libellula became an increasingly dominant prey in the diets of zooplanktivorous fish and seabirds, demonstrating the important role for T. libellula in the pelagic food web. Our analysis suggests that T. libellula is capable of controlling copepod populations, thus it may become a potential contributor to top-down regulation of Calanus spp. in the eastern Bering Sea.

Shifts in the dominance between diatoms and cryptophytes during three late summers in the Bransfield Strait (Antarctic Peninsula)

Recent global warming reduces surface water salinity around the Antarctic Peninsula as a result of the glacial meltwater runoff, which increases the occurrence and abundance of certain phytoplankton groups, such as cryptophytes. The dominance of this particular group over diatoms affects grazers, such as Antarctic krill, which preferentially feed on diatoms. Using three late summer data sets from the Bransfield Strait (2008–2010), we observed variations in the dominant phytoplankton groups determined by HPLC/CHEMTAX pigment analysis and confirmed by microscopy. Results indicate that the dominance of diatoms, particularly in 2008 and 2009, was associated with a deeper upper mixed layer (UML), higher salinity and warmer sea surface temperature. In contrast, cryptophytes, which were dominant in 2010, were associated with a shallower UML, lower salinity and colder sea surface temperatures. The low diatom biomass observed in the summer of 2010 was associated with high nutrient concentration, particularly silicate, and low chlorophyll a (summer monthly average calculated from satellite images). The interannual variability here observed suggests a delayed seasonal succession cycle of phytoplankton in the summer of 2010 associated with a cold summer and a late ice retreat process in the region. This successional delay resulted in a notable decrease of primary producers’ biomass, which is likely to have impacted regional food web interactions. This study demonstrates the susceptibility of the Antarctic phytoplankton community structure to air temperature, which directly influences the timing of ice melting and consequently the magnitude of primary production and succession pattern of phytoplankton groups.

Timing of the last deglaciation revealed by receding glaciers at the Alpine-scale: impact on mountain geomorphology

New Terrestrial Cosmogenic Nuclides (TCN) 10Be ages obtained on glacially polished rocks from the SW Alps (Tinée Valley, France) allow a comparison with ages obtained using similar methods for dating the deglaciation steps after the Last Glacial Maximum on the northern and southern sides of the Alps. The data presented in this study highlight three stages of glacial retreat on the southern flank of the Alps at remarkably similar ages that are 14.9 ± 0.8 10Be ka for the end of Oldest Dryas cold period, 10.9 ± 1.1 10Be ka for the end of Younger Dryas cold period and 8.4 ± 0.9 10Be ka for a late ice retreat stage. Previously published data from the Northern Alps lead also to an age of 15.7 ± 1.0 ka for the Oldest Dryas deglaciation, followed by the Younger Dryas at 11.3 ± 1.0 ka, and a late discrete ice retreat event at 9.7 ± 1.2 ka. The last glacial retreats occur thus simultaneously across the Alps and the deglaciation process was most likely unrelated to variations in latitude or to mountain flank exposition throughout the Alps. This may be ascribed to a relatively rapid climate change. Subsequent mountain slope evolution following the rapid glacier unloading is reflected by landslides and fault reactivation directly following the deglacial period. This temporal coincidence is ascribed to a cause-to-consequence effect of glacial unloading and water infiltration into tectonic and landslide triggering.

Climate change and control of the southeastern Bering Sea pelagic ecosystem

We propose a new hypothesis, the Oscillating Control Hypothesis (OCH), which predicts that pelagic ecosystem function in the southeastern Bering Sea will alternate between primarily bottom-up control in cold regimes and primarily top-down control in warm regimes. The timing of spring primary production is determined predominately by the timing of ice retreat. Late ice retreat (late March or later) leads to an early, ice-associated bloom in cold water (e.g., 1995, 1997, 1999), whereas no ice, or early ice retreat before mid-March, leads to an open-water bloom in May or June in warm water (e.g., 1996, 1998, 2000). Zooplankton populations are not closely coupled to the spring bloom, but are sensitive to water temperature. In years when the spring bloom occurs in cold water, low temperatures limit the production of zooplankton, the survival of larval/juvenile fish, and their recruitment into the populations of species of large piscivorous fish, such as walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus) and arrowtooth flounder (Atheresthes stomias). When continued over decadal scales, this will lead to bottom-up limitation and a decreased biomass of piscivorous fish. Alternatively, in periods when the bloom occurs in warm water, zooplankton populations should grow rapidly, providing plentiful prey for larval and juvenile fish. Abundant zooplankton will support strong recruitment of fish and will lead to abundant predatory fish that control forage fish, including, in the case of pollock, their own juveniles. Piscivorous marine birds and pinnipeds may achieve higher production of young and survival in cold regimes, when there is less competition from large piscivorous fish for coldwater forage fish such as capelin (Mallotus villosus). Piscivorous seabirds and pinnipeds also may be expected to have high productivity in periods of transition from cold regimes to warm regimes, when young of large predatory species of fish are numerous enough to provide forage. The OCH predicts that the ability of large predatory fish populations to sustain fishing pressure will vary between warm and cold regimes. The OCH points to the importance of the timing of ice retreat and water temperatures during the spring bloom for the productivity of zooplankton, and the degree and direction of coupling between zooplankton and forage fish. Forage fish (e.g., juvenile pollock, capelin, Pacific herring [Clupea pallasii]) are key prey for adult pollock and other apex predators. In the southeastern Bering Sea, important changes in the biota since the mid-1970s include a marked increase

Seasonal Variations of Sea Ice Extent in the Davis Strait-Labrador Sea Area and Relationships with Synoptic-Scale Atmospheric Circulation

Using published data sources for south-eastern Baffin Island, Ungava Bay and the northern Labrador Sea area, a study of the general patterns of sea ice growth and decay has been made for the years 1964 to 1974. From a comparison of individual years an "early" and a "late" pattern of both ice advance and ice retreat are recognized. Mean daily sea level pressure patterns for June - July and for October - mid-November are examined and a relationship is established between the type of ice advance or retreat pattern and the synoptic circulation over the area. In the years of early ice retreat there is an increased frequency of southerly airflow over the region. Strong winds and the advection of warm air leads to the more rapid removal of the ice compared to years of late ice retreat. Similarly for the years of early ice advance there is an increased frequency of northerly and westerly flow, bringing lower temperatures and an influx of second-year and multi-year ice into the area.