Responses in Arctic marine carbon cycle processes: conceptual scenarios and implications for ecosystem function

Figures & data

Fig. 1  Upper layer circulation in the Nordic seas and Arctic Ocean. Warm Atlantic inflow is shown with red solid lines, Arctic outflow with dashed red lines (A. Beszczynska-Möller, pers. comm.).

Fig. 2  The major internal pools and fluxes within the surface ocean, through which carbon can circulate: dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC) and particulate inorganic carbon (PIC); see Table 2 for details of the fluxes. The numbers in brackets in each box relate to the list of the five main carbon pools described in the text. Higher trophic level is abbreviated to HTL.

Table 1 Summary of pools and processes within the Arctic Ocean surface waters. Names and abbreviations are provided, as well as the source and sink pools (i.e., where carbon is transferred from and to) associated with each process.

Pools	A Autotrophs		P Abiotic particulate (POC, PIC) (detritus)
	H Heterotrophs (non-bacteria)		D Abiotic dissolved (DIC, DOC)
	B Bacteria (heterotrophic only)
	Flux	Process	Source	Sink	Net process
Biotic processes	F A,R	Autotrophic respiration	A-POC	DIC	F A,NP
	F A,P	Primary production	DIC	A-POC	F A,NP
	F A,C	Autotrophic calcification	DIC	A-PIC	F A,NC
	F A,D	Autotrophic dissolution	A-PIC	DIC	F A,NC
	F A,E	Autotrophic excretion	A-POC	DOC
	F B,R	Bacterial respiration	B-POC	DIC	F B,GE
	F B,P	Bacterial production	DOC,POC	B-POC	F B,GE
	F H,R	Heterotrophic respiration	H-POC	DIC
	F H,C	Heterotrophic calcification	DIC	H-PIC	F H,NC
	F H,D	Heterotrophic dissolution	H-PIC	DIC	F H,NC
	F H,S	Heterotrophic sloppy feeding	H-POC	DOC
	F H,F,B	Heterotrophic feeding on bacteria	B-POC	H-POC	F H,F
	F H,F,A	Heterotrophic feeding on autotrophs	A-POC	H-POC	F H,F
	F H,F,P	Heterotrophic feeding on particulates	POC	H-POC	F H,F
	F H,Fa	Heterotrophic faecal production	H-POC	POC
	F H,E	Heterotrophic excretion	H-POC	DOC
Abiotic processes	F P,P	Particulate production (death)	A-B-H-POC	POC
	F P,C	Particulate calcification (mineralization)	DIC	PIC	F P,NC
	F P,D	Particulate dissolution	PIC	DIC	F P,NC
	F PC	Photodegradation	DOC	DIC
	F FL	Flocculation	DOC	POC
External fluxes	F SE	Sedimentation/export to deep waters
	F G	Exchange with atmosphere
	F R	Exchange with rivers
	F O	Exchange with other oceans
	F U	Upwelling (exchange with deep waters)

Fig. 3  Mean monthly conditions for (a) incident photosynthetically active radiation (PAR), (b) air temperature (at 2 m), (c) wind speed, (d) sea surface temperature (SST), (e) sea-ice concentration, and (f) mixed layer depth (MLD) for each of the four case study regions. Data are averaged for the regions—Atlantic-influenced shelves (AiS), Pacific-influenced shelves (PiS), river-influenced shelves (RiS), and central basins (CB)—for the period 1979–2013 (for ice, air temperature and PAR, SST and wind speed) using National Centers for Environmental Prediction reanalysis data provided by the Physical Sciences Division of the Earth System Research Laboratory (National Oceanic and Atmospheric Administration) in Boulder, CO, from their website (http://www.esrl.noaa.gov/psd/) and for the period 1961–2008 for MLD, using MLD density-calculated climatology from de Boyer Montegut et al. (2004).

Fig. 4  (a) Relative fluxes of abiotic carbon into the Arctic Ocean (AO) over an average year from the main water inflows: Pacific Water (PW); Atlantic Water (AW) river water (RW). (b–d) relative flux of dissolved inorganic carbon (DIC), particulate inorganic carbon (PIC), dissolved organic (DOC) and particulate organic carbon (POC) into each of the focus regions within the AO: (b) Pacific-influenced shelves, (c) Atlantic-influenced shelves and (d) river-influenced shelves. Note the scales are different on the y-axis and PIC is estimated from a constant PIC:POC ratio of 0.67 (Striegl et al. 2007; McGuire et al. 2009).

Fig. 5  Relative size of extant (using data available in the literature between the years 1990 and 2013) pools and fluxes at each of the Arctic Ocean regions: (a) Pacific-influenced shelves, (b) Atlantic-influenced shelves, (c) river-influenced shelves and (d) the central basins. The pools include dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC) and particulate inorganic carbon (PIC), with the area of these boxes representing by the relative concentrations in µmol kg⁻¹ (except for PIC, where no data are available) and autotrophs (A), heterotrophs (H) and bacteria (B), with the size of these boxes representing the relative biomass in g C m⁻². Solid lines indicate fluxes for which there are data available, and are relative sizes in mg C m⁻² d⁻¹, except for the atmospheric CO₂ flux which is provided in Tg C y⁻¹. Dashed lines indicate fluxes where data are unavailable. Higher trophic level is abbreviated to HTL.

Fig. 6  Anomalies in (a) air temperature (AT), (b) sea-surface temperature (SST), and (c) ice cover (%) since 1979, relative to the 1979–2013 mean, for each of the Arctic ocean regions: Pacific-influenced shelves (PiS), Atlantic-influenced shelves (AiS), river-influenced shelves (RiS) and central basins (CB). Data are National Centers for Environmental Prediction reanalysis data provided by the Physical Sciences Division of the Earth System Research Laboratory (National Oceanic and Atmospheric Administration) in Boulder, CO, via the website http://www.esrl.noaa.gov/psd/.

Table 2 Ranges of values for each of the processes (flux as listed in Table 1), as available from the literature, for Pacific-influenced shelves (PiS), Atlantic-influenced shelves (AiS), river-influenced shelves (RiS) and central basins (CB).

Flux	Units	PiS	AiS	RiS	CB
F A,NP	mg C m^−2 d^−1	180–1630^a	200–500^b	20–359^c	50–140^d
F A,NC	Tg C y^−1	nd	0.48–1.59^e	nd	nd
F A,E	mg C m^−2 d^−1	11.0–98^f	12.0–30^f	1.2–22^f	4.5–156^f
F B,R	mg C m^−2 d^−1	44^g	105^g	21^g	69–664^g
F B,P	mg C m^−2 d^−1	6^h	18^i	7.8^j	6.0–57.7^k
F H,R		Dependent on zooplankton type
F H,NC		nd	nd	nd	nd
F H,S	mg C m^−2 d^−1	15–191^l	74–235^l	0.01–22^l	0.6–64^l
F H,F,B	mg C m^−2 d^−1	0.8^m	nd	nd	0.1–8.9^m
F H,F,A	mg C m^−2 d^−1	30–390^n	150–480^n	0.02–44.9^n	1–130^n
F H,F,P		nd	nd	nd	nd
F H,Fa	mg C m^−2 d^−1	nd	20–104^o	nd	0.4–1.7^p
F H,E	mg C m^−2 d^−1	1.8–23.5^q	9–28.8^q	0.001–2.64^q	0.08–8.3^q
F P,P	Gg C y^−1	nd	nd	nd	nd
F P,NC		nd	nd	nd	nd
F PC		nd	nd	66.5±18.5^r	nd
F FL		nd	nd	nd	nd
F SE	mg C m^−2 d^−1	90–970^s	70–240^s	5.6–239.9^s	0.9–31.2^s
F G	Tg C y^−1	Sink 11–53^t	Sink 44–77^t	Sink 1.0–5.7^t	Sink 6–9^t
F R	Sv				0.1
F O	Sv	0.8	2.2
F U

^aLee et al. 2013. ^bRey 2004. Loeng & Drinkwater 2007. ^cHirche et al. 2006. ^dOlli et al. 2007. ^eHovland et al. 2013. ^fCalculated from estimate of 6% primary production (F _A,NP) for PiS, AiS and RiS, 30% for CB. ^gCalculated from estimate of 12% bacterial growth efficiency (BGE) for PiS (avg. shelf/slope values [Kirchman et al. 2009]), 15% BGE for AiS, 8% BGE for CB (avg. CB values [Kirchman et al. 2009]) and 27% BGE for RiS (Meon & Amon 2004). ^hKirchman et al. 2009. ⁱHoward-Jones et al. 2002. ^jOrtega-Retuerta et al. 2012. ^kSherr et al. 2003. Wheeler et al. 1996. ^lCalculated from estimate of 49% C-intake. ^mCalculated from% bacterial production (F _B,P) (PiS 13–22%; CB 1.1–32%). ⁿCalculated from% PP (PiS 16–22%; AiS 75–95%; CB 6.7–25%). ^oRiser et al. 2002. ^pOlli et al. 2007. ^qCalculated from estimate of 6% C-intake. ^rTelang et al. 1991. ^sCalculated from% F _A,NP (PiS 50–60%; AiS 34–47%; RiS 28–66%; CB 6%). ^tBates & Mathis 2009.

Table 3 The potential impacts of change on physical, biogeochemical and ecological systems and the consequences for the carbon cycle, highlighting the regions—Pacific-influenced shelves (PiS), Atlantic-influenced shelves (AiS), river-influenced shelves (RiS) and central basins (CB)—most affected by each aspect.

Potential change	Consequences to physical, biogeochemical, and ecological systems	Potential impact on C cycle	Region	Ref.^a
River (land) influence
↑Freshwater discharge	· ↑ Stratification, ↓nutrients supply, ↓ F A,NP	↓ C drawdown in SW. ↓ C cycling	Mostly RiS, possibly some	1, 2
	· ↑ Nutrients supply, ↑ F A,NP,	↑ C drawdown in SW. ↑ C cycling	influence into the CB
	· Favour species tolerating low salinity,	?
↑Riverine supply of organic matter (old, refractory)	· ↓ Light, ↓ F A,NP	↓ C drawdown in SW. ↓ C cycling	RiS	3
	· ↑ Radiative heating or ↑ scattering	?		4
	· ↑ OM remineralization, ↓pH	↓ ocean CO2 sink		5
↑Supply of fresh (labile) organic matter	· ↑ Labile material, ↑ heterotrophic processes	↓ ocean CO2 sink	RiS	6
Oceanic influence
Major changes in sea-ice regime (switch from	· ↑ Coastal erosion, ↑ organic matter fluxes	(see river influences)	All, especially CB	2, 7
multi-year cover to seasonal ice cover)	· ↑ Vertical mixing, ↑ nutrient supply, ↑ F A,NP	↑ C drawdown in SW. ↑ C cycling
	· ↑ Vertical mixing, ↓ euphotic zone, ↓ F A,NP	↓ C drawdown in SW. ↓ C cycling
	· ↓ Ice cover, ↑ light availability, ↑ F A,NP	↑ C drawdown in SW. ↑ C cycling
	· ↑ Gas-exchange opportunities	Changes to C gas exchange
	· Changes in freshwater delivery	Changes to C gas exchange
	· Disturbed formation of cold water masses	Changes to C pump and export
	· Food web reorganization	Changes to C pump and export
↑Pacific inflow	· ↑ Nutrients supply, ↑ F A,NP,	↑ C drawdown in SW. ↑ C cycling	PiS (& CB)	8
	· ↑ Temperature, ↑ biological rates	Multiple level impacts
	· ↑ Advection of heterotrophs, ↑ grazing	↓ C drawdown in SW. ↓ C cycling
	· Water inflow further north, expands F A,NP	Larger area for C drawdown
↑Atlantic inflow	· ↑ Higher salinity water, ↑ stratification, ↓ nutrients supply, ↓ FA,NP	↓ C drawdown in SW. ↓ C cycling	AiS (& CB)	9
	· ↑ Temperature, ↑ biological rates	Multiple level impacts
Atmospheric influence
Atmospheric warming (air temperature ↑)	· ↓ Ice cover & volume (see ice changes above)		All	10
Oceanic warming (sea-surface temperature ↑)	· ↓ Ice cover & volume (see ice changes above)		All	2
	· ↑ Stratification, ↓ nutrients supply, ↓ F A,NP	↓ C drawdown in SW. ↓ C cycling
	· ↑ Temperature, ↑ biological rates	Multiple level impacts
↑Atmospheric CO2 concentration	· ↑ CO2 uptake, ↓ pH	Potentially alter ocean C sink, CaCO3 processes, biological C processes	All (depends on season and region)	11, 12, 13
Changes in large scale patterns of atmospheric circulation	· Changes in sea ice, ↑ precipitation, and change in cloud cover. Impact on light and mixing regimes	Multiple level impacts	CB (All)	14
Stratospheric ozone depletion	· ↑ UV radiation, ↓ F A,NP	↓ C drawdown in SW. ↓ C cycling	All	15
Increase in cloudiness	· ↓ PAR, ↓ F A,NP	↓ C drawdown in SW. ↓ C cycling	All	16

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