【Grant-in-Aid for Scientific Research (S)】Broad Section K
Title of Project： Global redistribution of heat, salt and materials induced
by sea-ice processes
OHSHIMA Keiichiro.
(Hokkaido University, Institute of Low Temperature Science, Professor)
Research Project Number: 20H05707
Researcher Number：30185251
Keyword：sea-ice production, sea-ice melt, microwave radiometer, bio-logging, thermohaline circulation【Purpose and Background of the Research】
Heat and salt/freshwater are redistributed by freezing andmelting of sea ice via latent heat and brine rejection (Fig.1).
Dense water formed by sea-ice production sinks and drives
the global thermohaline circulation. It is suggested that theAntarctic Bottom Water formed by high ice-production in
the Southern Ocean has decreased significantly (IPCC,AR5). Such deep/intermediate water change under the
global warming potentially affects the global thermohaline
circulation and thus earth climate. The deep/intermediatewater change with timescale of several decades is possibly
linked with variation of sea-ice production/melt. However,its linkage has not been clarified at all, because there havebeen no long-term data sets of ice production/melt so far.
The purpose of this study is to create a global 45-year data
set of ice production/melt and to elucidate the linkage
between ongoing deep/ intermediate water change andheat/salt transport by sea ice. Further, we aim atclarification of material transport processes by sea ice suchthat sediment/iron is incorporated into sea ice at theformation and its release at ice melting induces a large
phytoplankton bloom (Fig.1).

Figure 1: Global transport of heat, salt (freshwater), andmaterials (iron etc.) by sea-ice production and melt
【Research Methods】
Regarding sea-ice production, our team has developed themethod to detect high ice-production areas (coastalpolynyas) and to estimate sea-ice production there using
satellite microwave radiometer data first in the world.
However, the data sets have been made only for limitedareas and only after 2013 with the AMSR sensor. In thisstudy, we plan to develop pan-global algorithms of sea-ice
production for the four generation’s microwave sensors tocreate seamless 45-year data set since 1978. As comparison/validation data, our mooring data of sea ice and ocean atseveral coastal polynyas will be used. We will challenge
creation of ice-melt data set, which has never been made.

We combine the satellite microwave data, heat-budget
calculation, and high-resolution ice-drift data to infer icemelt amount. As comparison/validation data, data fromprofiling floats and bio-logging will be used. Further,intensive observations aboard the icebreakers and fisheryboats are planned in the southern part of the Okhotsk Sea
as a target area, with biogeochemical floats, to clarify therelationship between the phytoplankton bloom and icemelt.
【Expected Research Achievements andScientific Significance】
The 45-year data set of sea-ice production would provide
its linkage with ① Reduction of Antarctic Bottom Water,② Weakening of North Pacific overturning from theOkhotsk Sea, ③ Deep water formation in the Bering Sea,and the data set of sea-ice melt would provide its linkage
with ④ Freshening and density decrease of Antarctic
Intermediate Water. As such, the linkage between sea-ice
production/melt and intermediate/deep water change is
expected to be clarified. Because this global ice
production/melt data set will be the first one, the data set
is expected to be used as validation and boundary
condition data for various models. These will promote
understanding of role of sea-ice production/melt inclimate change. On the other hand, once processes ofmaterial/iron transport through sea ice will be understood,
those processes can be parameterized into the ice
production/melt data set, which will lead to understandingof global material/iron transport by sea ice.
【Publications Relevant to the Project】‧ Ohshima, K. I., S. Nihashi, and K. Iwamoto, Global
view of sea-ice production in polynyas and its linkage
to dense/bottom water formation. Geoscience Letters,
3:13, doi:10.1186/s40562-016-0045-4, (2016).
【Term of Project】FY2020-2024【Budget Allocation】151,700 Thousand Yen【Homepage Address and Other Contact Information】
http://www.lowtem.hokudai.ac.jp/wwwod/~ohshima/ohshima@lowtem.hokudai.ac.jp