Multiple climatic drivers increase pace and consequences of ecosystem change in the Arctic Coastal Ocean

Abstract

The impacts of climate change on Arctic marine systems are noticeable within the scientific “lifetime” of most researchers and the iconic image of a polar bear struggling to stay on top of a melting ice floe captures many of the dominant themes of Arctic marine ecosystem change. But has our focus on open‐ocean systems and parameters that are more easily modeled and sensed remotely neglected an element that is responding more dramatically and with broader implications for Arctic ecosystems? We argue that a complementary set of changes to the open ocean is occurring along Arctic coasts, amplified by the interaction with changes on land and in the sea. We observe an increased number of ecosystem drivers with larger implications for the ecological and human communities they touch than are quantifiable in the open Arctic Ocean. Substantial knowledge gaps exist that must be filled to support adaptation and sustainability of socioecological systems along Arctic coasts.

Full text

Limnology and Oceanography Letters 9, 2024, 683–695
© 2024 The Author(s). Limnology and Oceanography Letters published by Wiley Periodicals LLC
on behalf of Association for the Sciences of Limnology and Oceanography.
doi: 10.1002/lol2.10431
SYNTHESIS
Multiple climatic drivers increase pace and consequences of ecosystem
change in the Arctic Coastal Ocean
Mikael K. Sejr ,
1
*Amanda E. Poste,
2
Paul E. Renaud
3,4
1
Department of EcoScience, Arctic Research Center, Aarhus University, Aarhus C, Denmark;
2
Norwegian Institute for
Nature Research, Fram Centre for Climate and the Environment, Tromsø, Norway;
3
Akvaplan-niva, Fram Centre for
Climate and the Environment, Tromsø, Norway;
4
Department of Arctic Biology, University Centre in Svalbard,
Longyearbyen, Norway
Abstract
The impacts of climate change on Arctic marine systems are noticeable within the scientific“lifetime”of most
researchers and the iconic image of a polar bear struggling to stay on top of a melting ice floe captures many of
the dominant themes of Arctic marine ecosystem change. But has our focus on open-ocean systems and param-
eters that are more easily modeled and sensed remotely neglected an element that is responding more dramati-
cally and with broader implications for Arctic ecosystems? We argue that a complementary set of changes to
the open ocean is occurring along Arctic coasts, amplified by the interaction with changes on land and in the
sea. We observe an increased number of ecosystem drivers with larger implications for the ecological and
human communities they touch than are quantifiable in the open Arctic Ocean. Substantial knowledge gaps
exist that must be filled to support adaptation and sustainability of socioecological systems along Arctic coasts.
More than a third of the global coastline is found along the
three continents that encircle the Arctic Ocean (Carmack
et al. 2015). No single definition exists for the Arctic coastal
ecosystem, but here we use the Riverine Coastal Domain (RCD;
Carmack et al. 2015), defined as the contiguous 15 km wide
zone characterized by unique physical, chemical, and biological
conditions driven primarily by input of freshwater from land.
While there are obvious commonalities in ecological processes,
we argue that there are important contrasts between the RCD
and the open-ocean systems of both the Arctic Ocean and its
broad continental shelves. This paper aims to review the spe-
cific processes driving ecological changes in the Arctic coastal
ecosystem and to identify key knowledge gaps.
The classical view of the open Arctic Ocean marine ecosys-
tem posits a short-lived spring bloom of primary production
by microscopic phytoplankton, either associated with sea ice
or in the water column, where a significant proportion of the
total primary production can take place within a few weeks
(Wassmann et al. 1999). This production relies on inorganic
nutrients transported upward to surface waters. Phytoplank-
ton near the sunlit surface is consumed by zooplankton,
resulting in transfer to higher trophic levels and the sinking
of fecal pellets and aggregates of organic matter to the seafloor
where they sustain the benthic compartment (Wassmann and
Reigstad 2011). Processes are highly seasonal, driven by light
and nutrient availability and modified by the presence of sea
*Correspondence: mse@ecos.au.dk
Associate editor: Elise Granek
Author Contribution Statement: The authors contributed equally to all aspects of producing this manuscript.
Data Availability Statement: There is no original data presented in this paper.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any
medium, provided the original work is properly cited.
683

ice and snow cover. Thus, in open Arctic seas, climate change
primarily impacts the ecosystem through warming and sea-ice
loss, and their implications for light and nutrient availability
(Ardyna and Arrigo 2020). Primary production in the coastal
ocean ecosystem differs from offshore in that production in
the water column is supplemented by producers on the sea
floor. In the Arctic, light penetrates to the sea floor in many
areas and biomass of macroalgae can exceed 30 kg wet weight
m
2
(Sejr et al. 2021) with annual production rates of several
100s g C m
2
yr
1
(Pessarrodona et al. 2022), thus exceeding
area-specific biomass and productivity of phytoplankton by
orders of magnitude. The particulate and dissolved organic
matter generated by benthic production enters coastal food
webs and fuels biogeochemical cycles (Renaud et al. 2015a).
Furthermore, significant quantities of organic matter originating
from terrestrial ecosystems enter the coastal zone through river
discharge and shoreline erosion. Hence, the coastal ecosystem
relies on three main sources of organic matter (pelagic produc-
tion, benthic production, and terrigenous input), each of which
supports different types of consumers (Dunton et al. 2006;Har-
ris et al. 2018; McMeans et al. 2013). The contribution from
these two additional sources of carbon unique to the coastal
ocean is substantial. The total net pelagic production in the Arc-
tic Ocean by phytoplankton has been estimated from remote
sensing to be 540 10
6
tCyr
1
(Babin et al. 2015). The gross
annual benthic production of microphytobenthos is estimated
at 115 10
6
tCyr
1
(Attard et al. 2016), while the potential
net production by macroalgae is estimated to be 7300 10
6
tC
yr
1
(combining potential macroalgae area in the Arctic (Assis
et al. 2022) and the average Arctic macroalgal production
(Pessarrodona et al. 2022)). The input from land has been esti-
mated to be 18–26 10
6
tCyr
1
of dissolved carbon, 4–
610
6
tCyr
1
of particulate carbon from rivers (Dittmar and
Kattner 2003), and 6.7 10
6
tCyr
1
from coastal erosion
(Semiletov et al. 2011). There are smaller but locally important
contributions of organic matter from the Greenland Ice Sheet
(Lawson et al. 2014) and groundwater (Connolly et al. 2020).
All these estimates come with considerable uncertainty but
show that (1) the contribution of carbon sources unique to the
coastal ocean (benthic production and terrigenous carbon)
equals or possibly exceeds that of pelagic primary production of
the open ocean; and (2) for the coastal ocean there are periods
and habitats where these carbon sources dominate. Thus,
coastal ecosystems are sustained by organic matter whose bio-
availability, phenology, and response to climatic impacts are
vastly different than that of the pelagic ocean ecosystem.
At lower latitudes, it has long been recognized that
estuarine-coastal ecosystems provide extensive ecosystem ser-
vices for society but also are impacted by a unique combina-
tion of natural and anthropogenic forcings (Barbier
et al. 2011). The concept of meta-ecosystems defined as a set
of ecosystems linked by flows of energy, materials, and organ-
isms has been applied to describe the connectivity between
terrestrial processes and coastal ecosystems through the flow
of freshwater into estuaries (Loreau et al. 2003). This connec-
tivity can cause problems related to nutrient enrichment in
lakes, rivers, and streams, with subsequent eutrophication of
coastal waters being a key application (Cloern 2001). The lat-
eral export of terrestrial matter by rivers into the coastal zone
and subsequent horizontal gradients in density, light, and
nutrient dynamics created by the freshwater input mean that
focus is on lateral advection in coastal environments in con-
trast to the emphasis on the vertical fluxes in the open ocean.
This is especially relevant in the Arctic where warming
increases precipitation and snow and ice melt which increases
freshwater input into the ocean and intensifies the land-coast
coupling (Hernes et al. 2021). Taken together, these contrasts
in key ecosystem services such as productivity, connectivity,
harvestable resources, biodiversity, and uptake of greenhouse
gases suggest that the coastal ecosystem will respond along a
different trajectory and at a different pace than the open
Arctic Ocean.
Coastal change is more pronounced
Warming temperatures, sea-ice loss, and the cascading
effects on pelagic ecosystems are the “face”of Arctic Ocean
change (Wassmann et al. 2020). But coastal systems are
impacted by a broader set of drivers that are unique to, and/or
magnified in, the coastal region (Table 1). Four such drivers are
the modification of Arctic shorelines, glacial retreat, increased
freshwater runoff, and increased human activity (Fig. 1). Each
of these drivers, alone and in combination with other drivers,
have manifold consequences for specific ecosystem changes.
For example, in open-ocean systems warming and sea-ice melt
influence pelagic primary production via impacts on stratifica-
tion. Warming and melting throughout the cryosphere, com-
bined with increased runoff from land, have arguably greater
consequences for coastal primary production through their
impacts on stratification, underwater light fields, nutrient con-
centrations, and acidification (Demidov et al. 2023; Ether-
ington et al. 2007). Here, we argue that the limited evidence
available suggests most changes in large-scale drivers and their
ramifications for changes in environmental factors are more
pronounced in coastal than in offshore systems (Table 1).
Warming
Seawater temperatures are impacted by increasing atmo-
spheric temperatures and by local and regional processes,
including advected heat from ocean currents and from atmo-
spheric weather patterns. Modeling studies over the entire
Arctic basin predict greater warming within the top 200 m of
the water column will occur in nearshore regions (Renaud
et al. 2015b). River discharge also contributes heat to the
Arctic coastal zone, a mechanism that has contributed up to
10% of coastal sea-ice loss (Park et al. 2020). Suspended
sediments in river water entering the sea absorb solar radiation,
further warming coastal waters.
Sejr et al. Rapid change on Arctic coasts
684

Table 1. Overview contrasting change in key environmental drivers, ecosystem structure and function and societal impacts in the
near coastal zone and the offshore Arctic Ocean. Red shading indicates drivers or changes that are only (or primarily) relevant for the
coastal zone. Yellow shading indicates ecosystem changes where the direction of change and key drivers differ between near coastal
and offshore areas. Blue shading indicates a change that is occurring in the same direction in both near coastal and offshore areas, with
darker blue indicating where observed/predicted change is higher. Select key references are included in the table, while additional
references and details can be found in the main text.
Coastal zone Offshore
Environmental drivers
Warming Yes (IPCC 2019) Yes: although less than along coast
(Carvalho et al. 2021)
Changing cryosphere Yes: permafrost thaw, glacial melt, loss of land-fast
ice (Barnhart et al. 2014; Hernes et al. 2021)
Yes: sea-ice loss (Crawford et al. 2021)
Changing human activity Yes: particularly relevant for coastal environment
(Alvarez et al. 2020)
Yes: although less pronounced than for
coastal regions (Bartsch et al. 2021)
Shoreline change/erosion Yes (Irrgang et al. 2022)
Increased runoff Yes (Feng et al. 2021)
Ecosystem changes
Changing light availability Yes: trade-off between sea ice loss and increased
attenuation due to runoff (increased turbidity,
cDOM (Singh et al. 2022)
Yes: increased light availability due to
sea ice loss (Bélanger et al. 2006)
Freshening Yes: driven by terrestrial runoff (including from
glaciers) and sea-ice melt (Sejr et al. 2017)
Yes: driven by sea ice melt. Lower than
along coast.
Acidification Yes: driven by increased atmospheric CO
2
and
terrestrial runoff (dilution and geochemical
changes) (Henson et al. 2023)
Yes: driven by increased atmospheric
CO
2
and less sea ice (AMAP 2018)
Changes in organic matter (OM)
quantity and/or quality
Yes: driven by shifts in terrestrial runoff (Fichot
et al. 2013)
Likely, but less pronounced (driven by
changes in primary production and
OM mineralization)
Nutrients Increased due to terrestrial runoff (regionally
variable) (Meire et al. 2017)
Decreased due to increased
stratification. (Farmer et al. 2021)
Contaminants Increased Hg due to permafrost thaw (Chételat
et al. 2022)
Likely, but less pronounced (broad-scale
climate-driven changes in transport
and cycling of contaminants)
(AMAP 2021a)
Ecosystem responses
Pelagic primary production Yes: observed and predicted increases (strongest
along coast), due to riverine nutrients and sea-ice
loss. However, an unclear impact of changing
coastal light attenuation (Terhaar et al. 2021)
Yes: Observed and predicted increases,
due to sea-ice loss (also attributed to
changes in nutrient, and plankton
biomass) (Lewis et al. 2020)
Benthic primary production Yes: predicted strong increase (due to reduced land
fast ice) (Assis et al. 2022)
Changing species distributions Yes: due to warming, arrival of boreal species,
habitat changes. Risk for invasive species linked
to shipping (Renaud et al. 2015b)
Yes: especially due to loss of sea-ice
habitat (Michel et al. 2012)
Societal impacts
Infrastructure Yes: coastal erosion and permafrost thaw threaten
coastal infrastructure (Nielsen et al. 2022)
Safety Yes: unsafe ice; increased shipping traffic and
hazards; increasing trend in search and rescue
activities in some Arctic coastal areas (Ford
et al. 2021)
Yes: increased shipping traffic may
increase risk of accidents (Fu
et al. 2021)
(Continues)
Sejr et al. Rapid change on Arctic coasts
685

Cryosphere
The loss of sea ice, a key indicator of Arctic climate change,
has been well documented (Kwok 2018). Remote sensing stud-
ies have revealed pronounced increases in the duration of the
coastal open-water season, with typical increases ranging from
approximately 10–25 d decade
1
(Barnhart et al. 2014), in
contrast to the open Arctic Ocean with 5–6 d decade
1
(Crawford et al. 2021). Whereas the loss of sea ice has many
of the same effects in both coastal and open-ocean environ-
ments, the coastal zone is also impacted by changes in glaciers
Table 1. Continued
Coastal zone Offshore
Fisheries Yes: increased risk associated with subsistence
fishing from land-fast ice. Changing species
distributions impact coastal fisheries
(Galappaththi et al. 2019)
Yes: changing species distributions and
sea-ice conditions impact fisheries
(areas of activity and target species)
(Van Pelt et al. 2017)
Fig. 1. Schematic representation of the how climatic driven changes in both the ocean and terrestrial ecosystems amalgamate in the coastal ocean with
specificinfluence on the distribution and availability of light, nutrients, and organic matter which are key drivers of biogeochemical and biological
changes. Note that most of the strongest impacts (solid arrows) originate in the coastal zone and not the terrestrial or open-ocean regions, where direct
impacts are weaker (dotted arrows).
Sejr et al. Rapid change on Arctic coasts
686

and permafrost. In Greenland (King et al. 2020), for example,
the annual net mass-loss rate of the Greenland ice sheet has
increased sixfold since the 1980s (Mouginot et al. 2019). Glacial
meltwater entering the coastal region creates distinct physical
and biogeochemical gradients (Meire et al. 2017), with subse-
quent impacts on ecosystem structure and function (Hopwood
et al. 2020). With the continued retreat of glacial fronts, more
glaciers will eventually change from having the glacial front in
the ocean to having it on land. This change will profoundly
alter the delivery of meltwater with consequences for vertical
mixing, fjord circulation, and light and nutrient availability
(Hopwood et al. 2020). Permafrost thaw is also accelerating in
most Arctic regions and contributes to an increase in total river
discharge and the delivery of both organic and inorganic mate-
rials to the coast (Hernes et al. 2021).
Human activity
Ship traffic through the Arctic breaks ice to make shipping
lanes. A key emerging route is the northern sea route along the
Russian coasts where the number of annual transits has been
increasing exponentially, resulting in small-scale changes in ice
distribution, heat exchange, and light penetration, as well as
increasing vulnerability for introduction of non-native species
from ship hulls or ballast water discharge (Miller and Ruiz 2014).
This activity and its consequences are arguably more prevalent
in coastal regions where ice-breaking is concentrated around
ports and industrial installations. Coastal areas are also affected
by other human activities, including both local and regional
consequences of coastal infrastructure, fishing, tourism, petro-
leum, mining, and discharges of sewage (Vincent 2020), which
result in a stronger direct human footprint compared to the
open ocean. The continued loss of sea ice is increasing the
accessibility to the Arctic and is projected to result in greater
economic activity, with concurrent expansion of coastal infra-
structures (Alvarez et al. 2020).
Shoreline change
Shoreline change includes both coastal erosion and other
geomorphological dynamics, such as building and moving of
river deltas (Bendixen et al. 2017). The latter is little studied,
although changes in sedimentary environments can pro-
foundly alter the Arctic coastal region where these habitats
dominate. The erosion of Arctic coasts is accelerated by the loss
of sea ice and land-fast ice. As sea ice disappears, wind gener-
ates bigger waves, while melting of permafrost makes coastlines
more vulnerable to erosion. As a result, coastal erosion happens
throughout the Arctic and with rates that have increased by a
factor of 2–3 in recent decades (Nielsen et al. 2022). Erosion
has strong implications for the coastal ocean through the deliv-
ery of both organic matter and nutrients, and through its
impacts on coastal infrastructure. Coastal erosion delivers as
much organic matter to the ocean as all Arctic rivers combined
(Vonk et al. 2012;Wegneretal.2015) and the nutrients
released have been estimated to sustain about 20% of the
coastal primary production (Terhaar et al. 2021).
Runoff
Freshwater runoff into the Arctic Ocean has been estimated
to have increased by 0.22% per year since 1984 (Feng
et al. 2021) but with substantial regional differences. Impor-
tantly, much of this runoff is retained within the RCD.
Changing runoff patterns are strongly influenced by several of
the drivers already mentioned (warming, cryosphere loss), as
well as changes in precipitation patterns (Box et al. 2019). The
input of freshwater affects the coastal ocean in several ways,
including reduced salinities and increases in heat, nutrients,
organic matter (OM) and contaminants (Hernes et al. 2021).
The combination of these effects contributes to why the
response of coastal ecosystems to climate change will follow
different trajectories than those of the open ocean.
Light availability
Thinning and loss of both sea ice and land-fast ice will, all
else being equal, result in increased light penetration into the
water column, with profound consequences for marine pri-
mary producers. In nearshore habitats, however, increased
input of sediments and colored dissolved organic material
(cDOM) combined with resuspension and erosion may reduce
light penetration. A remote sensing analysis covering the Arc-
tic coastal ocean found that increased turbidity resulted in a
22% increase in light attenuation between 2003 and 2020,
largely canceling out the light enhancement caused by
decreasing ice cover (Singh et al. 2022). This provides a good
example of how dynamics in a central parameter controlling
ecosystem productivity are driven by different processes not
only with different outcomes in the coastal ocean compared
to open-ocean environments, but also with substantial local
and regional variability along Arctic coasts.
Acidification
Acidification of the oceans is driven by the uptake of CO
2
from the atmosphere and can impact cellular processes,
energy balance, and calcification potential in marine organ-
isms. The loss of sea-ice cover increases the area and seasonal
duration for air-sea exchange of CO
2
, making the Arctic espe-
cially vulnerable to acidification (Terhaar et al. 2020). The sol-
ubility of CO
2
is temperature dependent and warming will
moderate some of the acidification potential. Increased fresh-
water from riverine input and melting sea ice and glaciers
decreases seawater alkalinity and substantially exacerbates acid-
ification in coastal regions (Henson et al. 2023;Yamamoto-
Kawai et al. 2009). Thus, models for the end of the 21
st
century
predict declines in aragonite saturation state in the coastal Arc-
tic to be at least a factor of 5 greater than in the open Arctic
Ocean (Renaud et al. 2019). Photosynthesis, which takes up
CO
2
, and degradation of organic matter, which releases CO
2
,
contribute to significant spatial and seasonal variation in acidi-
fication in both habitats (Henson et al. 2023; Krause-Jensen
et al. 2015).
Sejr et al. Rapid change on Arctic coasts
687

Organic matter
Cycling of organic matter (OM) in offshore marine waters
is dominated by pelagic primary production and subsequent
food-web uptake, mineralization, vertical flux, and burial. In
the coastal zone, benthic primary production and both partic-
ulate and dissolved OM from land represent additional
sources of both autochthonous and allochthonous OM
(Canuel and Hardison 2016; Sejr et al. 2022). These are likely
to become increasingly important in response to climate
change due to the mobilization and land-ocean transport of
permafrost-derived OM (Frey and McClelland 2009;Wild
et al. 2019). The coastal sources of organic matter are, thus,
distinct in terms of their quantity and lability. Kelp forests
can form extremely high standing stocks that produce
substantial amounts of dissolved organic carbon with high
content of humic-like components, which reduce the bio-
availability compared to carbon from phytoplankton (Wada
et al. 2008). However, kelp forests are also an important
food source for pelagic and benthic food webs (Balmonte
et al. 2020;Renaudetal.2015a). The contribution of carbon
from different sources with different degrees of bioavailability
ultimately influences the production (via light availability;
Fichot et al. 2013) and the fate of the organic matter. This
has implications for how much of the organic matter pro-
duced and received in the coastal zone is sequestered and
thus, contributes to mitigating anthropogenic emissions of
CO
2
(Ager et al. 2023; Bélanger et al. 2006; Sejr et al. 2022).
In particular, the fate of the large quantities of terrigenous
OM delivered to Arctic coastal waters is largely unconstrained,
including the potential for mineralization of terrigenous
OM to lead to a positive climate feedback (Juranek 2022;
Parmentier et al. 2017).
Nutrients
Increasing stratification from warming in many areas of
the offshore Arctic Ocean is expected to reduce mixing of
deep, nutrient-rich waters to the surface (Farmer et al. 2021).
In the coastal zone, however, climate-change impacts on
nutrient availability are likely to vary strongly in both space
and time due to altered timing and magnitude of land-ocean
nutrient transport (linked to heterogeneity in bedrock geol-
ogy, catchment processes, and hydroclimatic conditions)
(Speetjens et al. 2023), as well as coastal dynamics (including
erosion, resuspension, stratification, and upwelling, Irrgang
et al. 2022). Recent studies from Greenland suggest that the
retreat of marine-terminating glaciers onto land will reduce
fjord productivity as the entrainment of deep, nutrient-rich
marine water into fjord surface waters by rising plumes of sub-
glacial discharge will be replaced by particle-rich, low-nutrient
surface runoff (Meire et al. 2023). In other areas, the impor-
tance of terrestrial runoff as a source of both organic and
inorganic nutrients to coastal and offshore waters may be sub-
stantial (McGovern et al. 2020; Terhaar et al. 2021; Wadham
et al. 2019).
Contaminants
Long-range atmospheric and oceanic transport of environ-
mental contaminants has resulted in global distributions of
persistent, bioaccumulative, and toxic compounds. Due to
global distillation processes, the Arctic experiences particularly
high deposition of semi-volatile chemicals transported from
warmer regions, leading to high concentrations of, for exam-
ple, polychlorinated biphenyls (PCBs) and mercury (Hg) in
Arctic marine food webs (AMAP 2021b). The immense water-
sheds, lakes, and rivers surrounding the Arctic Ocean all serve
to collect additional burdens of contaminants that are subse-
quently transported to the coastal ocean. Along the coast,
thawing permafrost and melting glaciers represent a growing
source of contaminants to food webs through increased mobi-
lization and land-ocean transport (Chételat et al. 2022). Given
that northern permafrost soils represent a globally significant
Hg pool, the potential for permafrost thaw to lead to
increased Hg contamination of the Arctic environment,
including its food webs, is of great concern (Lim et al. 2020).
Increasing human activity can also lead to significant point
sources of contaminants (including contaminants of emerging
concern) to the coastal environment, for example, from
industry and shipping-related activities and the release of
untreated wastewater (AMAP 2021a).
Coastal change has ecosystem consequences
Examination of key environmental drivers and their
response to climate change shows that the coastal ocean is
closely linked to terrestrial processes, which differentiates it
from the open ocean (Table 1). The additional drivers and
their rate of change warn that the accumulated pressure on
the coastal ocean system exceeds that in both bounding oce-
anic and terrestrial systems. Disentangling the spatial and
temporal mosaic of accumulated pressure from several drivers
is a key challenge if we are to improve current understanding
and capability to predict the response of coastal ecosystems to
warming. We point to runoff, freshening, glacial melt, and
coastal erosion (Fig. 1) as key drivers which, through impacts
on the availability of light, nutrients, and organic matter, can
alter coastal ecosystem structure and function. These bottom-
up effects will be supplemented by top-down effects, for
example, changes in the distribution and abundance of fish
species or marine mammals responding to increasing water
temperature and loss of sea ice (Heide-Jørgensen et al. 2023;
Kortsch et al. 2015).
The productivity of an ecosystem is one of its key charac-
teristics, and the projected changes in future conditions of
both coastal and offshore environments include reduced ice
cover, resulting in greater light availability. Remote sensing
studies have confirmed a general increase in productivity
driven by the loss of sea ice in offshore environments (Ardyna
and Arrigo 2020). Indeed, increased primary production is
both predicted and has been observed along the coast due to
Sejr et al. Rapid change on Arctic coasts
688

higher light levels and readily available nutrients from land
and sediment (Assis et al. 2022). Whereas primary production
in the open ocean is largely limited to pelagic phytoplankton,
both macroalgae and benthic microalgae are abundant in
coastal regions and are expected to increase their contribu-
tions to coastal primary productivity. As waters warm, ice
retreats, and the inorganic nutrient supply remains sufficient,
new habitats suitable for macroalgal growth can emerge
(Kortsch et al. 2012; Krause-Jensen et al. 2012). Reductions in
ice scour and increased light penetration have been observed
to increase macroalgal distributions into both shallower and
deeper waters, respectively (Castro de la Guardia et al. 2023;
Krause-Jensen et al. 2020), although increased turbidity from
glacial or riverine input may limit depth distribution locally
(Niedzwiedz and Bischof 2023) and in the Arctic in general
(Singh et al. 2022). Macroalgae are habitat-forming species
and can enhance not only productivity but also biodiversity
in areas where they expand. They also provide significant
quantities of organic matter that are integrated into nearshore
food webs (Renaud et al. 2015a), and potentially enhance car-
bon export and potential sequestration (Ager et al. 2023). Ben-
thic microalgae in shallow, coastal habitats can be highly
productive due to ample nutrients diffusing upward from the
sediments. In one Arctic fjord, it was estimated that benthic
microalgae in waters under 30 m depth exhibited primary pro-
duction values at the same order of magnitude as phytoplank-
ton (Rysgaard and Glud 2007). Benthic microalgae have also
been estimated to have production rates up to 5that of phy-
toplankton, and importantly, that the depth range over which
they could be active may extend well over 100 m depth
(Attard et al. 2016). These findings suggest that increased light
availability along Arctic coasts can greatly enhance the net
community primary productivity and local food-web subsidies
by expanding the depth ranges, spatial extent, and total pro-
duction of benthic microalgae and macroalgae (Attard et al.
2024). Local processes governing turbidity and the (changing)
timing of turbidity events will, in part, determine the extent
of productivity increases, and need further investigation. Sedi-
ments settling on the seafloor can change benthic habitats
and bury sedentary organisms but also carry organic matter of
varying lability that can be remineralized, buried in coastal
habitats, or may be readily consumed by benthic organisms
(Harris et al. 2018). It is increasingly clear that climate change
effects at the base of the food chain may be much more com-
plex and dramatic in the coastal oceans of the Arctic than in
open waters. The contributions of benthic primary producers
and terrigenous organic matter to coastal food webs need to
be better constrained before we can fully gauge the impact of
climate change on coastal ecosystems.
Climate drivers also directly affect community structure
and functioning in ways that appear to be exacerbated in
coastal waters. Establishment of boreal species via natural or
human-facilitated introduction is likely (Cottier-Cook
et al. 2024; Renaud et al. 2015b), although this may be less
prevalent along interior Arctic coastlines than in areas with
more direct linkages to temperate habitats. New community
assemblages generated by the establishment of non-native
species will have consequences that are difficult to predict
(Williams and Jackson 2007). Since many species introduc-
tions take place via maritime transport vectors, coastal areas
of the Arctic are more likely to be hotspots of invasions. That,
combined with the high habitat complexity in the coastal
ocean which provides more niches to potential invaders, sug-
gests that the coastal ocean will be more susceptible to the
establishment of alien species than the open ocean.
Warming will also lead to reductions and altered seasonal-
ity in shore-fast ice cover. This is likely to enhance scouring of
coastal habitats as remaining drift ice becomes more mobile.
Effects of ice scour are well documented, resulting in mosaics
of communities under different stages of recovery, with
impacts on both local structure and function, and enhanced
regional biodiversity (Conlan and Kvitek 2005). Where ice
scour is not relevant, warming can result in higher growth
rates of benthic species (Ambrose et al. 2006; Sejr et al. 2009)
and higher benthic biodiversity (Beuchel et al. 2006). The
increasing frequency of marine and terrestrial heat waves has
been linked to a range of biological effects, including a region-
wide shift in intertidal community structure along Alaskan
coasts (Weitzman et al. 2021). Metabolic rates within the
water column and at the seafloor will also likely increase due
to warming, resulting in higher carbon cycling rates and
organic matter degradation, with knock-on effects on oxygen
concentrations, nutrient regeneration rates, and the autotro-
phic/heterotrophic balance. Although these processes may
also be enhanced in the warming open ocean, differences in
habitat diversity and links with terrestrial processes and
human settlements are likely to result in more pronounced
impacts on current community structure, function, and ser-
vices provided in the coastal system (Fig. 2). Few of these sec-
ondary impacts of climate change will be felt in the open
ocean but may well characterize the changing coastal ecosys-
tem. Species at higher trophic levels such as fish, marine
mammals, and seabirds are concentrated along the coast and
are especially affected by changes to primary producers, prey
fields, and structural changes in the coastal ecosystem. And
changes in distribution and abundance of these organisms
will most directly impact human populations living in or
using the resources of the Arctic coastal seas.
Coastal change impacts people
Changes in coastal ecosystems will impact people living
there, but will also have far-reaching impacts. Arctic coastal
communities are a key element of strongly coupled socio-
ecological systems linking living resources from the coastal
ecosystem to communities throughout the Arctic and beyond.
Subsistence and commercial coastal fisheries and aquaculture
are substantial components of the economies of Arctic nations
Sejr et al. Rapid change on Arctic coasts
689

and contribute significantly to national exports and value
chains (Vincent 2020). Locally, many Arctic communities rely
on coastal marine resources for subsistence and have strong
cultural ties to the habitats and organisms present (Larsen
et al. 2021). Changes in the coastal cryosphere will interfere
with access to culturally and economically important hunting
and fishing activities. Higher contaminant loads from indus-
trial activities and mobilization following permafrost thawing
will have profound impacts on communities that are strongly
reliant on high trophic-level organisms such as fish, seabirds,
and marine mammals. Furthermore, living conditions, cul-
tural identity, and sense of place will be substantially altered
by shoreline change, loss of land-fast ice, and changes in
seasonality of key, culturally relevant species. If changes take
place at an accelerated pace, they may exceed the ability of
local communities to adapt (Hovelsrud et al. 2011). The open
shelf and the deep Arctic Ocean stand in stark contrast by
exhibiting few direct and indirect links with human
populations. Coastal changes will, therefore, have more direct
impacts on human societies than will changes in the open
ocean or outer shelf.
Sustainable management and adaptation actions require
better knowledge about how the accumulated pressures from
climate change affect living resources that sustain local liveli-
hoods and economies (Ford et al. 2021). As the melting of sea
ice continues to make the Arctic coasts more accessible,
Fig. 2. Conceptual figure showing the transition of the Arctic coastal zone with emphasis on the impact of melting of marine and terrestrial ice and
impacts on the coastal socioecological system.
Sejr et al. Rapid change on Arctic coasts
690

increased activities related to aquaculture, shipping, tourism,
energy production, and extraction of living and nonliving
resources are expected (Hovelsrud et al. 2011). The opportuni-
ties of the new Blue Economy increase the need to expand
infrastructures to support industry, search and rescue, and sci-
entific activities, resulting in a larger human footprint in the
coastal zone. This produces a feedback loop where environ-
mental manifestations of climate change alter many aspects
of coastal communities, resulting in further anthropogenic
change—challenges that may compound environmental
impacts. Similar to the ecological consequences of climate
change, these complex societal implications have been little
explored.
Conclusion
Above we review how climate change influences the coastal
ecosystem and argue it leads to a substantial footprint along
Arctic shores, impacting coastal ecosystems at a pace we
hypothesize exceeds that in both terrestrial and open-ocean
systems. This indirect human footprint is then combined with
the direct physical human footprint from roads, structures,
and industry, which has increased by 15% since 2000 (Bartsch
et al. 2021). In addition to the local impacts these changes
will have on Arctic communities, the vast geographic extent
of the coastal Arctic means that changes here have global
ramifications, including sea level rise, changes in ocean circu-
lation patterns and atmospheric greenhouse-gas feedbacks.
The Arctic has sustained humans for millennia and the ongo-
ing transformation of the coastal ecosystem threatens many
components of this socioecological system. We can no longer
reverse the accelerating effects of climate change in the near
future, which leaves adaptation as the inevitable alternative
for communities living there. This requires the best possible
prediction of what to expect and herein lies a clear challenge
for the scientific community. Coastal change is not always
well-represented in the dominant narratives of Arctic Ocean
change (i.e., a polar bear on an ice floe). This is highlighted by
the striking mismatch between the strong focus on open-
ocean change in key international reports focusing on the
physical, biogeochemical and ecological impacts of climate
change on the Arctic Ocean (IPPC 2019), and reports
highlighting the pressing need for knowledge related to cli-
mate change risks and adaptation needs for communities
along the pan-Arctic coast (AMAP 2021b). Arctic coastal
change is complex, pronounced and has profound impacts on
those living along the pan-Arctic coast. Meanwhile, the eco-
system models and remote sensing approaches applied for the
open Arctic Ocean are challenging to transfer to the dynamic
coastal environment, where high spatiotemporal variability
and interactions among multiple drivers complicate under-
standing of the compounding and amplifying effects of cli-
mate change. We argue that now is the time for a sustained
effort to develop the tools necessary to improve our
understanding and quantification of how climate change
affects the services provided by the vast Arctic coastal eco-
system. Existing tools that should be enhanced include
tailored coastal ecosystem models nested within larger
regional domains, remote sensing products developed and
validated for the coastal oceans, and use of drones to
increase the spatial and temporal resolution when rele-
vant. However, the biggest leap forward is likely to happen
when efforts are co-developed with local communities and
combine scientific approaches with residents’long-term
ecological expertise of local ecosystems. The spatial hetero-
geneity and temporal dynamics of the coastal zone will
require specific solutions for each question, emphasizing
the need for improved pan-Arctic exchange of already
existing knowledge and new data on Arctic coastal ecosys-
tem change.
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Acknowledgments
We highly appreciate the comments by Eddie Carmack on an early version
of this paper. The editors and two anonymous reviewers also provided very
insightful and constructive input which greatly improved the manuscript.
The authors were funded by the European Commission through the Polar
Ocean Mitigation Potential project (grant # 101136875). MKS was also
supported by a grant from the Aage V. Jensen Charity Foundation
(Greenland Coastal Biodiversity Reference Project). AP and PR were
supported through the Catchment to Coast (C2C) research program
funded by the Fram Centre (FRAM—High North Research Centre for
Climate and the Environment). The work presented in this article results in
part from funding provided by national committees of the Scientific
Committee on Oceanic Research (SCOR) and from a grant to SCOR from
the US National Science Foundation (OCE-1840868) to the Changing
Oceans Biological Systems project.
Submitted 19 September 2023
Revised 01 July 2024
Accepted 07 August 2024
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