Estimation of Sea Ice Production in the Bering Sea From AMSR‐E and AMSR2 Data, With Special Emphasis on the Anadyr Polynya

Abstract

We created, for the first time, a map of sea ice production in the Bering Sea, based on thin‐ice thickness data from the Advanced Microwave Scanning Radiometers (AMSR‐E and AMSR2) with a heat flux calculation. We used the AMSR‐E thin‐ice algorithm developed for the Arctic Ocean with some modification. We provided a 16‐yr data set of ice production from the 2002/2003 to 2018/2019 seasons, excepting the 2011/2012 season. It is found that the Anadyr polynya has by far the highest sea ice production (average of 93 km3/yr) and accounts for more than 30% of all polynya ice production in the Bering Sea. The combined ice production in the Anadyr, Anadyr Strait, and St. Lawrence polynyas becomes the second‐largest ice production during the AMSR‐E period in the Northern Hemisphere. It is considered that the high ice production in the Anadyr polynya produces cold, saline, nutrient‐rich water, so‐called Anadyr Water, which would contribute to the formation of the cold halocline layer and high biological productivity. The ice production in the Anadyr polynya shows very large year‐to‐year variability. The record low ice extent year of the 2017/2018 season is also the lowest ice production year; the production is only one tenth of the highest value, observed during the 2015/2016 season. The high sensitivity of the wind direction and strength to the location of the Aleutian Low causes this large variability. We also built reconstruction schemes of ice production in the polynyas, using the offshore wind and air temperature, by multiple linear regression.

Improved SSM/I Thin Ice Algorithm with Ice Type Discrimination in Coastal Polynyas

“…(Maykut and Perovich 1987) using bulk transfer coefficients that take into account the stability of the atmospheric surface layer (Kondo 1975). When sea ice thickness is small, thermal inertia can be ignored and thus a linear temperature distribution inside the sea ice can be assumed (Ohshima et al 2003). Therefore, net heat flux on sea ice surface balances with the conductive heat flux through the ice (FC).…”

“…1). In addition, we validate our new algorithm using 26 cases from three coastal polynyas and a marginal ice zone in the Arctic Ocean, which were used for development and validation of the previous algorithm for the Arctic Ocean (Iwamoto et al 2013(Iwamoto et al , 2014. Finally, we discuss the global applicability of the algorithm.…”

“…When seawater freezes, high-salt water (brine) is rejected from sea ice, forming cold dense shelf water (DSW). This DSW drives the meridional overturning circulation of the global ocean by sinking into the intermediate/deep layer, and it contributes to the formation of Antarctic Bottom Water (AABW) (Orsi et al 1999;Ohshima et al 2013) and North Pacific Intermediate Water (NPIW) (Warner et al 1996;Shcherbina et al 2003). DSW formation due to active ice production also affects the maintenance of the cold halocline layer in the Arctic Ocean (Cavalieri and Martin 1994).…”

“…Based on this characteristic, algorithms for classifying sea ice as new ice, young ice, and first-year ice were developed using the PR value and the gradient ratio (GR) of brightness temperatures at different frequencies derived from the Special Sensor Microwave Imager (SSM/I) in the Bering Sea (Cavalieri 1994) and the Sea of Okhotsk (Martin et al 1998;Kimura and Wakatsuchi 1999;Tateyama et al 2000). Ohshima et al (2003) later acquired the first quantification of sea ice production in the Okhotsk coastal polynyas by heat budget analysis, assuming a uniform sea ice thickness of 5 cm for new ice and 20 cm for young ice.…”

“…Martin et al (2004) compared the SSM/I PR values [strictly R values in their study; R 5 (1 1 PR)/(1 2 PR)] with ice thickness obtained from a heat budget analysis (Yu and Rothrock 1996;Drucker et al 2003) using ice surface data from the Advanced Very High Resolution Radiometer (AVHRR), and developed a thin ice thickness algorithm for the Chukchi coastal polynya in the Arctic Ocean. Based on such thin ice thickness (TIT) algorithms using SSM/I, the Advanced Microwave Scanning Radiometer EOS (AMSR-E), or the Advanced Microwave Scanning Radiometer 2 (AMSR2), sea ice thicknesses up to 20 cm were derived, and sea ice productions were quantified through heat budget analyses in the Southern Ocean (Tamura et al 2007(Tamura et al , 2008(Tamura et al , 2016Comiso et al 2011;Nihashi and Ohshima 2015;Nihashi et al 2017), the Arctic Ocean (Tamura and Ohshima 2011;Iwamoto et al 2013Iwamoto et al , 2014, the Sea of Okhotsk (Nihashi et al 2009;Kashiwase et al 2014), and the Bering Sea (Ohshima et al 2020). In addition, finer mappings of thin ice thickness and sea ice production were recently obtained using clear-sky infrared data from the Moderate Resolution Imaging Spectroradiometer (MODIS) in the Southern Ocean (Paul et al 2015) and the Arctic Ocean (Preußer et al 2016).…”