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"Spring Bering Sea."
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Arctic marine mammal population status, sea ice habitat loss, and conservation recommendations for the 21st century
Arctic marine mammals (AMMs) are icons of climate change, largely because of their close association with sea ice. However, neither a circumpolar assessment of AMM status nor a standardized metric of sea ice habitat change is available. We summarized available data on abundance and trend for each AMM species and recognized subpopulation. We also examined species diversity, the extent of human use, and temporal trends in sea ice habitat for 12 regions of the Arctic by calculating the dates of spring sea ice retreat and fall sea ice advance from satellite data (1979–2013). Estimates of AMM abundance varied greatly in quality, and few studies were long enough for trend analysis. Of the AMM subpopulations, 78% (61 of 78) are legally harvested for subsistence purposes. Changes in sea ice phenology have been profound. In all regions except the Bering Sea, the duration of the summer (i.e., reduced ice) period increased by 5–10 weeks and by >20 weeks in the Barents Sea between 1979 and 2013. In light of generally poor data, the importance of human use, and forecasted environmental changes in the 21st century, we recommend the following for effective AMM conservation: maintain and improve comanagement by local, federal, and international partners; recognize spatial and temporal variability in AMM subpopulation response to climate change; implement monitoring programs with clear goals; mitigate cumulative impacts of increased human activity; and recognize the limits of current protected species legislation.
Journal Article
Enhanced relationship between February Aleutian low and spring extreme consecutive dry days in the Yangtze-Huai River region in recent two decades: roles of Bering Sea ice and stratospheric polar vortex
This study analyzes the interannual relationship between preceding winter Aleutian low (AL) and spring extreme consecutive dry days (extreme-CDDs) in the Yangtze-Huai River region (YHR) during 1979–2019. The results show that, independent from the El Niño-Southern Oscillation variability, a weakened AL in February is accompanied by more spring extreme-CDDs in YHR. Additionally, such a relationship shows a remarkable decadal enhancement after the late-1990s, in which the changes in the Bering Sea ice (BSI) and stratospheric polar vortex (SPV) play bridging roles. On the one hand, the weakened AL could lead to decreased BSI in spring during the whole period by inducing anomalous warm-moist air transport and the resultant radiation effect. After the late-1990s, the decreased BSI could cause a stronger anomalous high over Lake Baikal in spring by exciting an eastward propagated atmospheric wave train, favoring downward motions and more extreme-CDDs in YHR. On the other hand, after the late-1990s, the weakened AL could induce an intensified SPV persisting from late February to early spring by inhibiting the upward propagation of planetary wave. The SPV signal could in turn propagate downward to the troposphere, also contributing to anomalous high over Lake Baikal in spring and more extreme-CDDs in YHR. In contrast, the stratosphere-troposphere interaction associated with anomalous AL is weak before the late-1990s. Through the above-mentioned physical processes, the February AL could have a significantly lagged impact on spring extreme-CDDs in YHR after the late-1990s, consequently providing valuable prediction source for the variability of spring extreme-CDDs in YHR.
Journal Article
Changes in the factors controlling Northeast Asian spring surface air temperature in the past 60 years
Exploring the predictability sources of Northeast Asian spring surface air temperature (NEAST) is of great socioeconomic importance. In the present study, three factors that alternately take control of NEAST during different epochs in the past 60 years are identified. Specifically, NEAST was found to be closely associated with the Arctic Oscillation (AO) in 1961–1994 (E1), the rainfall over the tropical Indian Ocean (RIO) in 1995–2004 (E2), and the tripole pattern of North Atlantic sea surface temperature (NAT) in 2005–2020 (E3). During E1, zonally elongated barotropic cyclonic anomalies associated with the negative phase of the AO led to negative NEAST. During E2, negative diabatic heating related to suppressed RIO stimulated a Rossby wave train propagating from the Arabian Sea to Northeast Asia, resulting in barotropic cyclonic anomalies in the region and negative NEAST. During E3, positive diabatic heating anomalies in the extratropical North Atlantic induced by NAT caused two quasi-barotropic Rossby wave trains over the mid-to-high latitudes of continental Eurasia. The Rossby wave trains both ended with a barotropic cyclonic anomaly over Northeast Asia, leading to negative NEAST. Further analyses show that the rapid decline in Arctic sea-ice cover in the Sea of Okhotsk and Bering Sea in the mid-1990s, weakening of the central Asian westerly jet, and enhancement of NAT-related rainfall anomalies around the mid-2000s, were responsible for the changes in the factors controlling NEAST. A physical-based empirical model constructed using the three identified factors and their precursors nicely reproduced and forecasted the variation in NEAST, outperforming the hindcast of the coupled dynamical models.
Journal Article
Sea ice directs changes in bowhead whale phenology through the Bering Strait
Background
Climate change is warming the Arctic faster than the rest of the planet. Shifts in whale migration timing have been linked to climate change in temperate and sub-Arctic regions, and evidence suggests Bering–Chukchi–Beaufort (BCB) bowhead whales (
Balaena mysticetus
) might be overwintering in the Canadian Beaufort Sea.
Methods
We used an 11-year timeseries (spanning 2009–2021) of BCB bowhead whale presence in the southern Chukchi Sea (inferred from passive acoustic monitoring) to explore relationships between migration timing and sea ice in the Chukchi and Bering Seas.
Results
Fall southward migration into the Bering Strait was delayed in years with less mean October Chukchi Sea ice area and earlier in years with greater sea ice area (
p
= 0.04, r
2
= 0.40). Greater mean October–December Bering Sea ice area resulted in longer absences between whales migrating south in the fall and north in the spring (
p
< 0.01, r
2
= 0.85). A stepwise shift after 2012–2013 shows some whales are remaining in southern Chukchi Sea rather than moving through the Bering Strait and into the northwestern Bering Sea for the winter. Spring northward migration into the southern Chukchi Sea was earlier in years with less mean January–March Chukchi Sea ice area and delayed in years with greater sea ice area (
p
< 0.01, r
2
= 0.82).
Conclusions
As sea ice continues to decline, northward spring-time migration could shift earlier or more bowhead whales may overwinter at summer feeding grounds. Changes to bowhead whale migration could increase the overlap with ships and impact Indigenous communities that rely on bowhead whales for nutritional and cultural subsistence.
Journal Article
Phytoplankton Bloom Changes under Extreme Geophysical Conditions in the Northern Bering Sea and the Southern Chukchi Sea
The northern Bering Sea and the southern Chukchi Sea are undergoing rapid regional biophysical changes in connection with the recent extreme climate change in the Arctic. The ice concentration in 2018 was the lowest since observations began in the 1970s, due to the unusually warm southerly wind in winter, which continued in 2019. We analyzed the characteristics of spring phytoplankton biomass distribution under the extreme environmental conditions in 2018 and 2019. Our results show that higher phytoplankton biomass during late spring compared to the 18-year average was observed in the Bering Sea in both years. Their spatial distribution is closely related to the open water extent following winter-onset sea ice retreat in association with dramatic atmospheric conditions. However, despite a similar level of shortwave heat flux, the 2019 springtime biomass in the Chukchi Sea was lower than that in 2018, and was delayed to summer. We confirmed that this difference in bloom timing in the Chukchi Sea was due to changes in seawater properties, determined by a combination of northward oceanic heat flux modulation by the disturbance from more extensive sea ice in winter and higher surface net shortwave heat flux than usual.
Journal Article
First Data on the Distribution, Some Features of Ecology and Size Composition of Rock Greenling Hexagrammos lagocephalus (Hexagrammidae) in the Southwestern Bering Sea during the Winter-Spring Period
Based on the materials collected during the monitoring of bottom trawl fishery, the data on the distribution, thermal habitat conditions and size composition of the rock greenling
Hexagrammos lagocephalus
in the southwestern Bering Sea in the winter-spring period are presented for the first time. The main sites of catches of this species are located in areas with a complex bottom relief, mainly at protruding capes at depths of 134–498 m at a near-bottom layer of water temperature of 0.5–3.8°C. High frequency of occurrence and catches in February–March were recorded in the range from 201–400 m, while in April–May, a gradual migration of some fish to the shelf was observed. It was found that rock greenling is not characterized by spatial changes in the size composition, and the catches are mainly formed by medium-sized individuals with a total length of 39–47 cm. The results of the analysis of the length–weight relationship of fish in the southwestern Bering Sea in comparison with that in the Pacific waters off Kamchatka and the northern Kuril Islands may indicate a similar growth pattern of rock greenling in adjacent waters.
Journal Article
Mechanisms of Persistent High Primary Production During the Growing Season in the Chukchi Sea
Persistent high primary production during the growing season in the Chukchi Sea (Arctic Ocean) plays a key role in maintaining an efficient biological carbon pump and diverse Arctic ecosystem. We used a three-dimensional ocean–sea ice–biogeochemical model to simulate monthly averaged net primary production from 1998 to 2015. The results show that the growing season in the Chukchi Sea lasts more than 150 days, with an annual net primary production of 30.85 ± 3.67 Tg Cy⁻¹. The mechanisms for maintaining high primary production differ in the southern and northern Chukchi Sea biological hotspots. Nutrient-rich Pacific Winter Water triggers phytoplankton blooms in both hotspots as light intensity increased in spring. After these initial blooms, Bering Summer Water and remnant Pacific Winter Water are the main contributors to nutrient levels and drive primary production during the growing season (May to September) in the southern and northern hotspots, respectively. Nitrate budget estimations in the euphotic zone reveal that after the spring blooms, persistent high primary production in the southern hotspot is mainly fueled by advecting Bering Summer Water through the Bering Strait. In the northern area, vertical mixing plays a critical role in upwelling nutrient-rich Pacific Winter Water from around the Hanna Shoal, where Pacific Winter Water is trapped for a long duration as a result of topography-influenced ocean circulation. Hence, high primary production exists in the northern Chukchi Sea during the summer and early autumn.
Journal Article
Life Cycle Characteristics and Distribution of Giant Grenadier Coryphaenoides pectoralis (Macrouridae) in Northwest Bering Sea
The outcomes from the survey research in distribution of the giant grenadier
Coryphaenoides pectoralis
at different stages of development in the Northwest Bering Sea over 1963–2020 have been reported. The data for 37 thousand catches performed with the bottom and multi-depth trawls at the depths between 0–1200 m are processed. It has been revealed that the species fish tend to spawn throughout the year, with two periods of peak spawning activity in the second half of a spring season and from the late summer season to the first half of an autumn season. The female fish ready to spawn migrate down the water column, keeping deeper than 600 m, where the males ready to spawn are concentrated. After spawning, they come back to the feeding areas of less water depths. The juvenile giant grenadier less than 30 cm in length can be encountered in the mesopaelagic and upper bathypelagic zones, which do not appear to form dense aggregations. The majority of the specimens less than 30–40 cm in length and smaller commonly leave this water column layer to occupy the bottom water layers along the continental shelf. Such differentiation between the juvenils and the sexually mature specimens can provide the opportunity to avoid cannibalism and to use the habitat food sources efficiently.
Journal Article
Time-series of direct primary production and phytoplankton biomass in the southeastern Bering Sea
Sub-Arctic and Arctic regions are warming faster than nearly all other areas of the global ocean, leading to significant changes in ice quality and the duration of ice-covered periods. The impacts of this warming and sea ice variability on higher trophic levels in the Bering Sea is well documented, but the effects on lower trophic levels are less well understood. Phytoplankton biomass (as chlorophyll a [chl a]) and primary and nitrogen production measurements in the Bering Sea are presented from 2006−2016, a period that covers relatively colder (2007−2012) and warmer (2014−2016) temperature regimes. In warm spring periods, relative to cold spring periods, the frequency of subsurface chl a maxima increased, but with no significant differences in integrated chl a inventories. In contrast, cold fall periods were characterized by greater integrated chl a inventories than warm fall periods. Integrated net primary production (NPP) increased from the cold period (2007−2011) to the warm period (2014−2016). The difference in patterns in chl a and NPP resulted in higher phytoplankton growth rates during warm periods. Nitrate uptake rates in - creased from spring to fall during cold periods, while rates decreased from spring to fall during warm periods, suggesting changes in the balance of new versus regenerated production. While changes in phenological timing cannot be ruled out, changes in phytoplankton growth rate appear more important than changes in chl a biomass underlying increasing daily NPP. This distinction directly impacts our understanding of the linkages between warming temperatures and phytoplankton production and its implications in evaluating and understanding energy flow to higher trophic levels.
Journal Article