The MOSAiC ice floe: sediment-laden survivor from the Siberian shelf
Authors: Krumpen Thomas , Birrien Florent , Kauker Frank , Rackow Thomas , von Albedyll Luisa , Angelopoulos Michael , Belter H. Jakob , Bessonov Vladimir , Damm Ellen , Dethloff Klaus , Haapala Jari , Haas Christian , Harris Carolynn , Hendricks Stefan , Hoelemann Jens , Hoppmann Mario , Kaleschke Lars , Karcher Michael , Kolabutin Nikolai , Lei Ruibo , Lenz Josefine , Morgenstern Anne , Nicolaus Marcel , Nixdorf Uwe , Petrovsky Tomash , Rabe Benjamin , Rabenstein Lasse , Rex Markus , Ricker Robert , Rohde Jan , Shimanchuk Egor , Singha Suman , Smolyanitsky Vasily , Sokolov Vladimir , Stanton Tim , Timofeeva Anna , Tsamados Michel , Watkins Daniel 
Published: July 2020

Abstract. In September 2019, the research
icebreaker Polarstern started the largest multidisciplinary Arctic expedition to date,
the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic
Climate) drift experiment. Being moored to an ice floe for a whole year,
thus including the winter season, the declared goal of the expedition is to
better understand and quantify relevant processes within the
atmosphere–ice–ocean system that impact the sea ice mass and energy budget,
ultimately leading to much improved climate models. Satellite observations,
atmospheric reanalysis data, and readings from a nearby meteorological
station indicate that the interplay of high ice export in late winter and
exceptionally high air temperatures resulted in the longest ice-free summer
period since reliable instrumental records began. We show, using a
Lagrangian tracking tool and a thermodynamic sea ice model, that the MOSAiC
floe carrying the Central Observatory (CO) formed in a polynya event north
of the New Siberian Islands at the beginning of December 2018. The results
further indicate that sea ice in the vicinity of the CO (<40 km
distance) was younger and 36 % thinner than the surrounding ice with
potential consequences for ice dynamics and momentum and heat transfer
between ocean and atmosphere. Sea ice surveys carried out on various
reference floes in autumn 2019 verify this gradient in ice thickness, and
sediments discovered in ice cores (so-called dirty sea ice) around the CO
confirm contact with shallow waters in an early phase of growth, consistent
with the tracking analysis. Since less and less ice from the Siberian
shelves survives its first summer (Krumpen et al., 2019), the MOSAiC
experiment provides the unique opportunity to study the role of sea ice as a
transport medium for gases, macronutrients, iron, organic matter,
sediments and pollutants from shelf areas to the central Arctic Ocean and
beyond. Compared to data for the past 26 years, the sea ice encountered at
the end of September 2019 can already be classified as exceptionally thin,
and further predicted changes towards a seasonally ice-free ocean will
likely cut off the long-range transport of ice-rafted materials by the
Transpolar Drift in the future. A reduced long-range transport of sea ice
would have strong implications for the redistribution of biogeochemical
matter in the central Arctic Ocean, with consequences for the balance of
climate-relevant trace gases, primary production and biodiversity in the
Arctic Ocean.