now that the ice edge regularly retreats north
ofthe shelf break ( 12 , 13 , 30 )andstormshave
become more frequent and intense ( 31 ).
Despite substantial sea ice loss, there are
still regions of the AO, including much of the
interior and outflow shelves, where there was
either no change or a decline in Chlaconcen-
tration between 1998 and 2018. Apart from
the few areas of the shelf break where Chla
was enhanced, Chlagenerally declined across
most of the interior shelves (Fig. 1B and
Table 1). These waters receive large volumes
of low-nutrient and highly turbid river runoff
( 30 , 32 ), which suppresses NPP across the
interior shelves ( 30 ). For example, the Kara
subregion, which exhibited a significant 22%
decline in Chla(Fig. 1B and Table 1), has
received an increasing amount of discharge
from two of the three largest AO rivers (the
Yenisey and the Ob) ( 32 ) that has been doc-
umented to suppress NPP on the Kara shelf
( 33 ). Similarly, the outflow and interior shelves
may receive increasingly nutrient-depleted
surface water from upstream consumption
by phytoplankton on the productive inflow
shelves, resulting in a decline in NPP down-
stream ( 2 ).
Previously, it was unclear whether NPP
increases in the AO, which were linked only
to increases in OW area and duration, were
sustained by new or recycled nutrients ( 2 , 3 ).
Our study documents sustained increases in
NPP between 1998 and 2018 that are no longer
being driven by increased OW area and dura-
tion alone; increased phytoplankton concen-
tration is playing an increasingly important
role. These biomass increases must be sus-
tained by a larger supply of new nutrients to
the system. To the extent that increases in new
nutrient availability are driven by processes
associated with anthropogenic climate change,
the future AO may become not only more pro-
ductive but also more able to support addi-tional higher trophic-level production and
carbon export ( 34 ).REFERENCES AND NOTES- T. F. Stockeret al., Eds.,Climate Change 2013: The Physical
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SCIENCEsciencemag.org 10 JULY 2020•VOL 369 ISSUE 6500 201
Fig. 2. AO time series trends.(AtoC)Annual
time series of AO (A) mean OW area, (B) mean
Chla, and (C) NPP. Results from regression analysis
for the entire (1998–2018), early (1998–2008),
and recent (2009–2018) parts of the time series are
in black, red, and blue, respectively, with significant
trends (P< 0.05) indicated by an asterisk.
Table 2. Relative importance in predicting AO NPP.Multiplelinear regression parameter estimates (± standard error) for the intercept (teragrams of
carbon per year), OW area (ratio of teragrams of carbon per year to square kilometer), and Chlaconcentration (ratio of teragrams of carbon per year to
milligrams Chlaper cubic meter) in explaining the variance in mean annual NPP (teragrams of carbon per year) across the AO for entire time series
(1998–2018), first decade (1998–2008), and the most recent decade (2009–2018).Parameter Estimateb Pvalue Relative importance (%)
Entire time series............................................................................................................................................................................................................................................................................................................................................Intercept –247.7 ± 36.4
Coefficient of determination
(R^2 ) = 0.931OW area 6.92 × 10−^5 ± 6.88 × 10−^6 <0.01 57.27
............................................................................................................................................................................................................................................................................................................................................
............................................................................................................................................................................................................................................................................................................................................Chla 301.1 ± 37.09 <0.01 42.73(^1998) ............................................................................................................................................................................................................................................................................................................................................– 2008 Intercept –139.7 ± 58.43
R............................................................................................................................................................................................................................................................................................................................................^2 = 0.865 OW area 6.10 × 10−^5 ± 9.52 × 10−^6 <0.01 74.45
............................................................................................................................................................................................................................................................................................................................................Chla 191.8 ± 47.9 <0.01 25.55
(^2009) ............................................................................................................................................................................................................................................................................................................................................– 2018 Intercept –195 ± 69.84
R............................................................................................................................................................................................................................................................................................................................................^2 = 0.933 OW area 4.86 × 10−^5 ± 1.22 × 10−^5 <0.01 19.95
.....................................................................................................................................Chla .......................................................................................................................................................................................................381.5 ± 4.28 <0.01 80.05
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