In:
Biogeosciences, Copernicus GmbH, Vol. 18, No. 5 ( 2021-03-10), p. 1689-1701
Abstract:
Abstract. The North Atlantic north of 50∘ N is one of the most intense ocean
sink areas for atmospheric CO2 considering the flux per unit area, 0.27 Pg-C yr−1, equivalent to −2.5 mol C m−2 yr−1. The northwest
Atlantic Ocean is a region with high anthropogenic carbon inventories. This
is on account of processes which sustain CO2 air–sea fluxes, in
particular strong seasonal winds, ocean heat loss, deep convective mixing,
and CO2 drawdown by primary production. The region is in the northern
limb of the global thermohaline circulation, a path for the long-term deep-sea sequestration of carbon dioxide. The surface water masses in the North
Atlantic are of contrasting origins and character, with the
northward-flowing North Atlantic Drift, a Gulf Stream offspring, on the one hand and on the
other hand the cold southward-moving low-salinity Polar and Arctic waters with
signatures from Arctic freshwater sources. We have studied by observation
the CO2 air–sea flux of the relevant water masses in the vicinity of
Iceland in all seasons and in different years. Here we show that the highest
ocean CO2 influx is to the Arctic and Polar waters, respectively,
-3.8±0.4 and -4.4±0.3 mol C m−2 yr−1. These waters are CO2 undersaturated in all seasons. The
Atlantic Water is a weak or neutral sink, near CO2 saturation, after
poleward drift from subtropical latitudes. These characteristics of the
three water masses are confirmed by data from observations covering 30 years. We relate the Polar Water and Arctic Water persistent undersaturation and
CO2 influx to the excess alkalinity derived from Arctic sources.
Carbonate chemistry equilibrium calculations clearly indicate that the
excess alkalinity may support at least 0.058 Pg-C yr−1, a significant
portion of the North Atlantic CO2 sink. The Arctic contribution to the
North Atlantic CO2 sink which we reveal was previously unrecognized.
However, we point out that there are gaps and conflicts in the knowledge
about the Arctic alkalinity and carbonate budgets and that future trends in
the North Atlantic CO2 sink are connected to developments in the
rapidly warming and changing Arctic. The results we present need to be taken
into consideration for the following question: will the North Atlantic continue to
absorb CO2 in the future as it has in the past?
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-18-1689-2021
DOI:
10.5194/bg-18-1689-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2158181-2
Permalink