Coupled 3D SINMOD Models show that Primary Production, Secondary Production, and Sea-Ice Cover will be affected by Global Warming

The rise of temperatures in the Arctic is predicted to change ice cover, primary production, and secondary production.  Warmer air temperatures will melt existing ice.  Primary production depends upon ice cover and nutrient availability, which is influenced by climate-sensitive oceanographic processes.  Secondary production is correspondingly linked to the amount of primary production taking place.  Slagstad et al. used a physically-biologically coupled 3D SINMOD model to measure the extent and severity of these effects.  The SINMOD model was paired with atmospheric forcing data from the European Centre for Medium-Range Weather Forecasts (ECMWF) to produce five scenarios, or cases; an increase by 2, 4, 6, 8 C, and present day.  As temperature increased, the ice cover decreased.  Salinity and nutrient abundance differed by area.  Gross primary production increased in most areas of the Arctic, but to a lesser extent on the Canadian and Greenland shelves.  It remained constant in the Barents Sea, which may become the major source of gross primary production in the Arctic.  The model used two species of mesozooplankton to represent how secondary production might change.  Calanusfinmarchicus, a sub-Arctic species, will continue to flourish in the Barents Sea as well as spread eastward along the Eurasian shelf boundary.  C. glacialisand other Arctic species may move further north.  A species not factored into the model, C. hyperboreus, could possibly thrive in warmer Arctic waters. —Katherine Recinos  
Slagstad, D., Ellingsen, I.H., Wassmann, P., 2011.  Evaluating primary and secondary production in an Arctic Ocean void of summer sea ice: An experimental simulation approach. Progress in Oceanography 90, 117—131.
Climate change will cause a greater increase in temperature in the Arctic than for the rest of the world; 68 C as opposed to 13 C over the next 100 years.  This rise in temperature could, and will, have serious effects Arctic marine ecosystems.  The authors wanted to investigate how exactly the Arctic Ocean and surrounding sub-Arctic seas (Barents, Chukchi, shelf waters) might shift, both in terms of oceanographic-physiological process and biologic populations.  For this purpose they used the abovementioned coupled SINMOD model.  The SINMOD model is actually a system of models, including ones for hydrodynamics, ice, chemistry, and planktonic food web.  The hydrodynamic model incorporates an ice model that takes into account average ice thickness and ice compactness.  The planktonic food web, or ecological, sub model accounts for nitrate, ammonium, silicate, diatoms, autotrophic flagellates, bacteria, heterotrophic nanoflagellates, microzooplankton, fast sinking detritus, slow sinking detritus, dissolved organic carbon, bottom sediment, and two representative mesozooplankton: C. finmarchicus (sub-Arctic)and C. glacialis(Arctic).  The model used a horizontal grid with a 20 km grid point distance and 25 vertical levels starting 10 m below the water surface.  It also incorporated current velocities, four tidal variables, heat flux, dissolved organic material, freshwater flux, initial ice distribution, water temperature, and salinity.  The temperature of the air, often referenced as T NPair (from an ECMWF equation), is the variable which was increased in the experiment.
Slagstad et al. reaffirmed that as air temperature increases, sea ice cover decreases, especially in sub-Arctic seas.  At temperature increases of 6 C and 8 C (Case IV and Case V), there will be no ice during the summers and many sub-Arctic seas could begin to experience near ice free winters, such as the Barents Sea.  Water temperature and salinity were also looked at, but they are highly variable.  The most important results concerned primary and secondary production.  In the central Arctic Ocean and Eurasian shelf, gross primary production increased from 1030 gCm-2y-1 to 4060 gCm-2y-1.  It also increased in the Chukchi Sea, the East Siberian Sea, and Siberian shelf.  As stated in the introduction, gross primary production did not change much in the Barents Sea, because production increased in the northern part while decreasing in the southern part.  Areas of the Eurasian and Siberian shelves near rivers will experience less growth in primary production because river runoff reduces gross primary production.  There is a “band” near Canada and Greenland where gross primary production will decrease from 60 gCm-2y-1to 10 gCm-2y-1.  The net primary production, for all the models, is around 65% of the gross primary production.          
As temperature increases, the receding ice cover will trigger earlier plankton blooms, which play a role in increasing primary production.  This leads to a corresponding increase in secondary production at lower latitudes and the highest latitudes, and a reduction in secondary production in the mid-latitudes of the Arctic.  Higher temperatures will also stratify the waters and even reinforce the halocline in some areas.  The central Arctic Ocean will become much more saline at the surface due to freshwater.  Stratification reduces nutrient availability for primary production.  The two secondary producers factored into the model are affected in different ways.  C. finmarchicus will remain in the Barents Sea, suggesting that other sub-Arctic mesozooplankton could be unaffected or even benefit from a rise in temperature.  C. finmarchicus will also extend its range eastward along the Eurasian shelf following currents.  C. glacialiswill retreat northward, and may get pushed out of the Barents Sea.  As previously mentioned, a third mesozooplankton species, C. hyperboreus, could potentially survive in areas with no summer ice; moving in to replace more sensitive species. 
The authors discuss the flaws of the experiment.  Advanced models and more base data are needed.  New models could better incorporate physical forcing and mesozooplankton adaptation to new climates among others.  Sea ice algae was not factored into this model, yet plays a big part in primary production.  The grid size could be smaller to more accurately predict ice cover.  They note that the model seems to work very well for the Barents Sea, but it less accurate for other areas of the Arctic.  The results are too highly variable at times.  Further experiments need to be done to better understand the effects of climate change on Arctic marine ecosystems.                           

Rising Temperatures will Release Methane Hydrates into the Ocean and Atmosphere

There are large deposits of methane hydrates stored in sediments in shallow Arctic waters along continental shelves.  Methane is a greenhouse gas that can cause rapid global warming; scientists estimate that its effects are 25 times greater in magnitude than CO2.  Additionally, methane can affect Arctic Ocean water pH and oxygen content.  When the methane hydrates escape from the benthic sediments, they turn into methane gas.  As global temperatures warm, the bottom water in the Arctic could correspondingly rise, which would trigger the release of these methane hydrates.  25 % of hydrates are in shallow and mid-depth waters.  Rupke et al. used models to predict both the current temperatures of Arctic bottom water and the future temperatures 100 years from now.  Looking at the gas hydrate stability zone (GHSZ), where hydrostatic water pressure is greater than temperature and salinity dependent dissociation pressure, they determined that changes it its thickness will cause the release of both structure one and structure two hydrates.  Structure one and two hydrates have different molecular structure and therefore act differently and are unstable under different conditions.  12% of the total estimated 100 Gt C of methane at a sulfate reduction zone thickness of 5m is predicted to be released into the ocean and atmosphere.  This will cause little effect on the climate but could raise the pH and hasten oxygen depletion in the Arctic Ocean .Katherine Recinos
Rupke, L., Biastoch, A., Treude, T., Riebesell, U., Roth, C., Burwicz, E., Park, W., Latif, M., Boning, C., Wallmann, K., 2011. Rising arctic ocean temperatures cause gas hydrate destabilization and ocean acidification. Geophysical Research Letters 38.

The authors investigated how the temperature of Arctic bottom waters would change in relation to overall warming.  They used a hindcast with the ocean/sea-ice NEMO by the DRAKKAR collaboration.  This was compounded with a global simulation at ½ degree resolution (ORCA05) and 46 levels.  A repeated-year forcing scenario was subtracted from this model.  This gave the researchers a map of current water temperatures with deeper oceanic strata and exposed shelves having colder water.  A coupled climate model called KCM was then used at a 2 degree ORCA2 31 level resolution.  An atmospheric model, ECHAM5 [15] was used to model changes in the atmosphere.  These models generated eight 100 year global warming simulations and a 430 year control experiment.  They used a 1% increase in CO2 and present day CO2 levels respectively.  It took around 50 years for steady trends to develop, but the results showed a pan-Arctic increase of around 2.5 °C per century with the greatest changes along the continental slopes and on the shelves.     

As previously mentioned, there are two types of hydrates found in the Arctic; structure I and structure II.  Most of the effects considered in this paper are on structure one hydrates, however both types of hydrates are predicted to be affected, especially in shelf regions.  Rupke et al. then estimated the amount of hydrates present in Arctic sediments; 900 Gt carbon found north of 60° latitude under a 5m hydrate free zone.  The amount of hydrates found globally is estimated at 500-64,000 Gt C.  The total methane hydrates that would be released by a greater than or equal to 20 meter decrease in the gas hydrate stability zone would be 100 Gt C, but in the next 100 years only about 12% of that amount will actually be released.  Some of the released methane hydrates could become a sediment based carbon sink through microbial anaerobic oxidation (AOM).  The remaining methane will travel up through the water column and pass into the atmosphere.  On its way some will be transformed into CO2 and will lower ocean water pH by as much as 0.25 units.  Combined with acidification from increased CO2 in the atmosphere, oceanic pH could decrease by around 0.6 units. 

Mathematical Modeling of Sea-Ice Extent and Primary Production Shows Changes in Pelagic-Benthic Coupling

Pelagic benthic coupling is one of the most important processes in the Arctic Ocean and relatively little has been done to investigate the effects of climate variability on it.  Pelagic-benthic coupling depends on vertical flux and is influenced by sea ice thickness, extent, and patterns of formation and melting.  Vertical flux is the distribution and transportation of nutrients throughout the water column.  It is determined by primary production, zooplankton feeding, and physical oceanography processes.  Three conceptual biogeochemical models were used to investigate future ecosystem scenarios in the European Arctic Corridor, a region crucial for carbon cycling in the Arctic.  The first looked at climate changes effects on the timing of sea ice formation and melting and the corresponding phytoplankton blooms taking into account water stratification.  The second looked at the same thing but factored in vertical export of the bloom.  The third took into account the three areas of Arctic Ocean: open ocean (alpha ocean), seasonal ice zone (beta ocean), and multiyear ice zone.  Climate change will affect the beta ocean the most, and some areas may even turn into alpha ocean.  There will a longer period with no sea ice overall, which will extend ice algae and phytoplankton blooms.  Primary production will decrease, and this will decrease the yields of fisheries because of less vertical flux. Smaller phytoplankton will flourish.  The remaining vertical flux will be less seasonal in nature because of the dissolution of traditional sea-ice cycles. —Katherine Recinos         
Wassmann, P., and M. Reigstad, 2011. Future Arctic Ocean seasonal ice zones and implications for pelagic-benthic coupling. Oceanography 24, 220–231.

Wassmann and Reigstad state that there has been an ongoing lack of research on the Arctic, especially about pelagic-benthic coupling.  This is because the Arctic is hard to access and pelagic-benthic coupling differs from region to region in the Arctic Ocean and is thus hard to accurately measure in one study.  However, mathematical models have been developed which take biological, physical, and chemical data and create an overall picture for environmental scenarios in the Arctic Ocean.  Wassmann and Reigstad advocate the use of these models, and use three in this paper.  These are either adapted from other studies, or created by the authors specifically for this study.
Climate change will affect the extent of sea-ice in the Arctic which is intrinsically linked to the growth of sea-ice algae.  The importance of this algae depends on the area of ocean in consideration, but it plays a role in vertical flux and as a food for benthic organisms.  If the amount of sea-ice decreases, the blooms of ice algae will shift, leading the water to become more stratified, subsequently decreasing primary production.  This may happen in the Barents Sea.
A lengthening of the season with no sea-ice will lead to earlier phytoplankton blooms as well as ice algae blooms.  This will shift traditional patterns of nutrient consumption by zooplankton and trigger earlier vertical flux.  The vertical flux will be stretched out over a greater time frame which will lead to less pulsed pelagic-benthic coupling but more steady overall levels.  There will not be an increase in nutrients.  
Wassmann and Reigstad discuss alpha, beta, and multiyear ice oceans in terms of a warming climate.  Beta oceans will undergo the greatest changes and possibly adopt the characteristics of alpha oceans.  Vertical flux and productivity will decrease due to stratification.  The authors give examples of further studies to be done including collecting remotely sensed data on phytoplankton distribution and temperature-dependant respiration in areas with slowly increasing temperature.     

Atmospheric and Advective Forcing will affect the Physical and Biological Properties of the Barents Sea

 Between 2005 and 2008, the Norwegian Component of the Ecosystem Studies of Sub-Arctic Seas (NESSAS) studied atmospheric and advective forcing on the Barents Sea using retrospective analysis and modeling.  Atmospheric processes such as the North Atlantic Oscillation (NAO) and seasonal cyclones affect temperature and salinity in the Barents Sea.  Advection from the North Atlantic and surrounding Sub-Arctic seas also affects temperature and salinity. (Drinkwater 2011)  These variables in turn determine the sea-ice extent.  There is a corresponding affect on fisheries and primary production. Positive NAO, a greater number of cyclones, and advection of warmer water produce a warmer Barents Sea with less sea-ice. (Drinkwater 2011)  This leads to increased primary production and greater fisheries.  Additionally, in a warmer climate spawning sites will shift, fish populations will expand or retreat northward, and maturation will be faster. (Drinkwater 2011)   These effects were compared to other seas at similar latitudes to the Barents Sea. Many similarities in responses to forcing and overall biological processes were observed.  NESSAS recommends that further studies be carried out to better determine the effects of climate change on Sub-Arctic seas. —Katherine Recinos         
Drinkwater, K., 2011. The influence of climate variability and change on the ecosystems of the Barents Sea and adjacent waters: Review and synthesis of recent studies from the NESSAS Project. Progress in Oceanography. 90, 47-61.

The NESSAS program, as previously mentioned, was the Norwegian version of the more regional Ecosystem Studies of Sub-Arctic Seas (ESSAS) program.  The goals of both programs were the same; to examine how forcing, especially climate processes, effect physical oceanography, to look at how change affects marine ecosystems, and to see within those ecosystems how variability affects productivity and fish stocks.  The results could be used to combat future climate change.  The Norwegian program also compared the Barents Sea to other Arctic and Sub-Arctic seas.
                                                                                                          
Drinkwater begins with an overview of the NESSAS results.  Researchers looked at the NAO which has both a positive and negative phase.  During the positive phase, strong winds and storms blowing westward carry warm air and Atlantic water into the Barents Sea.  During the negative phase, the winds are weaker; cold air and less Atlantic water are carried into the Barents Sea.  The result is that positive phase NAO means higher sea temperatures in the Barents Sea and negative phase NAO means lower sea temperatures.  Sea temperature affects how much ice forms and when it forms and melts which has important ecological consequences.  
The NAO is associated with North Atlantic and Arctic cyclones.  The NESSAS studies investigated the patterns of cyclones that affect the Barents Sea.  An annual correlation was found between times of more intense Arctic cyclones and greater sea-ice cover.  However, longer term sea-ice extent was determined by North Atlantic cyclones with a one to two year lag from presence of cyclones to noticeable effects on sea-ice.  These effects are caused by the cyclones transporting different temperature waters into the Barents Sea. 
A different type of forcing is moisture flux which controls the amount of freshwater input from rivers, runoff, and precipitation.  Cyclones in northern latitudes play a role in moisture flux in Arctic and Sub-Arctic oceans and seas.  Seasonal variability affects the influence of the cyclones on moisture flux; there is a greater link between moisture flux and cyclone activity in the spring, summer, and autumn.  Atmospheric pressure patterns which produce cyclones and storms may also be changing.  The Arctic/North Atlantic Oscillation (AO/NAO) pressure pattern used to have three centers of action but now has only two more northerly centers.  This is leading to less atmospheric forcing and therefore a warmer Arctic overall.  
Drinkwater then discusses the effects of advection on the Barents Sea.  Not only does advection have the power to bring water of different temperature and varying salinities to the Barents Sea, it can also carry phytoplankton, zooplankton, and fish larvae to the Sea.  Several studies were carried out as part of NESSAS to try and figure out what factors determine advection, and how advection specifically works on the Barents Sea and surrounding oceans.  There are a series of differing salinity water masses known as the Great Salinity Anomalies (GSAs) which are either negative or positive anomalies.  A gradient across the northwest to northeast Atlantic controls their movements.  Due to advection, these water masses can affect Arctic waters and their respective salinities which affect, among other things, sea-ice formation.  Other studies used moors to monitor the flow of water into the Barents Sea.  This advection is important because it has major effects on the temperature of Barents Sea water, including heat fluxes.  It is affected by cyclones, storms, seasonal variability, and the NAO.
The NESSAS study also looked at biological effects.  The NORWECOM model, a coupled 3-D physical, chemical, and biological ocean model was used to examine primary production.  The North Atlantic coastal waters and the waters off the coast of Norway had the highest primary production.  Variability in primary production over the years was stated to be caused by the NAO.  When the NAO is high, there is more mixing, a greater concentration of nutrients, and therefore greater production.  When the NAO is low, the opposite is true.  Researchers investigated the future of fish stocks by looking at past data on fish populations.  A period of climate variability, the Atlantic Multidecadal Oscillation (AMO), produced a warming period in the 20thcentury that resulted in greater numbers of fish, northward spread of fish populations, changes in spawning areas, changes in timing of spawning, and faster growth and development for many cold-water species (ex. cod).  It also caused an increase in primary production which helped increase fish abundance. 
Drinkwater lists the results of comparative studies undertaken by NESSAS.  The Barents Sea is experiencing similar effects from atmospheric forcing as other seas at similar latitudes and would be similarly affected by climate change.  Many of the trends noted in the Barents Sea were also seen in other seas including advections affect on salinity and temperature, relationship of sea-ice to primary production, and spread of fish northward as temperatures increase. 
The NESSAS study admits uncertainty where climate change is concerned.  If warming continues, there could be a multitude of effects on fisheries, including increased yields.  For example, one study showed that capelin (a small fish) spawning sites would move further north and east in the Barents Sea.  The effects of climate change on physical properties of the Barents Sea could be mitigated by conflicting atmospheric processes such as the AMO and AMOC which could bring colder, saltier waters to the Arctic and Sub-Arctic.      

Changes in Sea Ice and Advective Flow will affect the Productivity of the Arctic Ocean

The effects of climate change on marine ecosystems in the Arctic have rarely been studied collectively.  As part of the 4th International Polar Year, Paul Wassmann gathered together the results of years of studies to investigate the major effects that climate change is having on arctic marine ecosystems and to postulate what studies could be done to further advance our scientific knowledge of the region.  The basic processes and features of arctic marine ecosystems that will be affected are the seasonal ice zone (SIZ), advective flow and regulation, the relationship between the blooming of primary producers and their consumption by secondary producers, pelagic-benthic coupling, and diversity and distribution of species. Conceptual and coupled physical-biological ecosystem models were used to determine that primary production will increase in certain areas but will remain stable overall, fisheries production will not increase, and that the stratification of arctic waters may actually decrease Arctic Ocean productiveness in the longer term.  Additionally, ice and phytoplankton algae may experience longer blooms which will decrease vertical export of nutrients and change food webs.  Although freshwater advection will facilitate the ability of fish to survive arctic winters, as the ecosystem decreases in salinity, plankton and smaller organisms will prosper. (Wassmann 2011)  To monitor these effects, further research needs to take place in the Fram Strait, the Siberian shelf, and the Central Arctic Ocean.  Studies need to encompass all seasons, and the time series analysis framework is recommended. (Wassmann 2011)—Katherine Recinos  
Wassmann, P., 2011. Arctic marine ecosystems in an era of rapid climate change. Progress in Oceanography. 90, 1-17.

Wassmann begins with an overview of where studies have been done in the Arctic Ocean region.  Most of the major regions, such as the Barents Sea and the Canadian Arctic Archipelago have data available from between two to eleven studies.  However, there is a dearth of knowledge from the Eastern Siberian Sea and accompanying shelf caused in part by the withholding of information by Russia and the general disorganization of studies that have been carried out there.  Of the Arctic Ocean studies that research is available from, the abovementioned processes and features are being effect by climate change: seasonal ice zone (SIZ), advective flow and regulation, the relationship between the blooming of primary producers and their consumption by secondary producers, pelagic-benthic coupling, and diversity and distribution of species.  Many of these processes are intrinsically linked; regional and time variation studies have determined that the SIZ will be affected by global warming, which will change blooming patterns among primary producers, which will then change nutrient distribution among water strata.  This would subsequently affect pelagic-benthic coupling and species biodiversity.  Wassmann gives an example from a study involving Calanus glacialis, a copepod.  C. glacialis depends on the ice algal and pelagic algal blooms for food, and its life cycle is timed according to traditional seasonal patterns.  Pelagic algal bloom is “governed to a larger degree by ice thinning and less predictable ice breakup.”  As the timing of the bloom changed, C. glacialis biomass decreased.  This effect of autotroph blooming on secondary producers is highly variable and can be seen across a number of species. 
Wassmann then describes the effects of advection on the Arctic Ocean.  Water is predicted to enter the Arctic Ocean from two main sources: the warmer ocean further south, and freshwater rivers.  This has the dual effect of increasing water temperature and decreasing salinity.  Marine ecosystem biomes and stratification of water by salinity will change in response.  Tests for carbon in sediment and nutrients such as nitrogen in the water show that ecosystem productivity is already being affected in some regions as a result.  A warmer Arctic Ocean could also attract species originally native to further south and facilitate the breeding of those that already live there (ex. the Arctic Cod).  It also limits the amount that primary production can increase because although there will be an increase in light, there will be an increase in secondary producers. 
Climate change effects on arctic marine ecosystems are usually modeled one of two ways, conceptually or numerically.  The numerical model described in this paper is a type of coupled physical-biological ecosystem model.  It looks at how chemical and oceanographic variables could affect biological processes and species dynamics.  Data from a number of studies using these models was collected and summarized by Wassmann.  The major trends and expectations extrapolated are those in the introduction paragraph. 
Wassmann concludes with a discussion of what further research should be done.  The Fram Straight, the central Arctic Ocean, and the Siberian ice shelf are areas where little to no research has been conducted.  More data is also needed on Arctic weather, SIZ, and “large-scale regulation of ecosystem function.” (Wassmann 2011)  Time series analysis would be beneficial as they allow scientists to see trends over time, but it is often difficult and expensive to do annual studies in one of the world’s harshest environments.  Wassmann advocates for the continued application of the physical-biological coupled 3D SINMOD and remote sensing models and the implementation of comparative studies.  International cooperation paired with these techniques will help scientists continue to observe the exact effects of climate change on the Arctic Ocean.  

Tipping elements in the arctic marine ecosystem

As global temperatures rise, they can trigger tipping points in marine ecosystems.  A tipping point is defined for the purposes of this article as “the critical point in forcing at which the future state of the system is qualitatively altered.” (Duarte et al. 2012)  Basically, a tipping point is a set of conditions or change in conditions that decisively transform the marine ecosystem.  Arctic marine ecosystems are especially sensitive, and relatively small changes in conditions could effectively act as tipping points. Duarte et al. discuss how climate change could alter global temperatures enough that arctic water temperatures and ice formation cycles would be pushed past their tipping points.  Since both of these variables are interconnected with the marine ecosystem at large, this could lead to biological change and possibly biological tipping points.  If water temperature and ice formation change, it would put stress on Arctic top predators which would have “cascading” effects on other populations which may eventually affect processes like air-sea CO2 exchange.   Theoretical tipping points in permafrost levels, methane hydrates levels, ocean biogeochemistry, the Greenland ice sheet composition and formation, and in arctic terrestrial ecosystems are analyzed for their effects on arctic marine ecosystems, especially the abovementioned changes.  It is unknown when, or whether, any tipping points will actually occur but the best estimate would be within the next few decades.—Katherine Recinos
Duarte, C.M., Augusti, S., Wassmann, P. Arrieta, J.M., Alcaraz, M., Coello, A., Marba, N., Hendriks, I.E., Holding, J., Garcia-Zarandona, I., Kritzberg, E., Vaque, D., 2012. Tipping elements in the arctic marine ecosystem. AMBIO: A journal of the human environment 41, 44–55.

Duarte et al. use data from a series of other studies to discuss the possibility of tipping points in arctic marine ecosystems.  The environmental tipping points considered are: air and seawater temperature, sea ice, Greenland ice sheet and glaciers, permafrost, arctic ozone layer, human activity, boreal forest dieback, peat desiccation decomposition and burning, ocean acidification.  They have effects ranging from increasing CO2to sea level rise, to changes in albedo.  These are not predicted to happen for decades to centuries.  The biological tipping points considered are: increased primary production, shift from diatoms to picoautotrophs, enhanced community respiration relative to production, decline of calanus glaciaris, decline of apical consumers, decline in vulnerable calcifying species, and loss of sea-ice community.  They have effects ranging from structural changes in food webs to ocean acidification.  These are not predicted to happen for decades.  However, Duarte et al. admit that not enough is known to accurately date these effects or if they will take place for certain.  There are already noticeable changes taking place within these categories, but it is still unclear if tipping points or thresholds will be crossed.       
If either the environmental or biological tipping points are crossed, it could have significant effects on arctic marine ecosystems.   Duarte et al. cite multiple studies on the how changes in temperature difference and ice formation would affect primary production.  This in turn would change marine food webs and composition of species.   Loss of ice would also affect top predator populations which would have a trickle-down effect.  A drastic change in temperature, or even in many cases a more subtle one, would directly affect species at all places in the food web by causing “poleward displacement.” 
Duarte et al. state that changes in the marine ecosystem could then lead to changes in chemical and biological processes such as air-sea CO2exchange and presence of CO2in different strata of water.  As the Arctic warms, it will also be more appealing and available for human use.  A greater human presence poses all the usual risks to marine life including chemical and oil spills and overfishing.  The authors conclude by warning that even though the tipping point might not be imminent, climate change has already been reshaping arctic ecosystems.

Rising Temperatures will Affect Primary and Secondary Production and Change the Nature of Pelagic-Benthic Species Relationships in the Pacific Arctic and Sub-Arctic

As temperatures rise due to global warming, changes in the formation of sea ice and water temperature in the Pacific Arctic will influence the entire marine ecosystem. A reduced amount of sea ice cover and an earlier retreat is predicted to either increase or decrease primary production. Warmer water temperatures and the possible increase in phytoplankton available as nutrients are causing a shift in the species composition of zooplankton, the secondary producers. Because conditions are increasingly favorable further north, zooplankton species that would normally be found in more temperate waters have been recorded in the Pacific Arctic and Sub-Arctic (Grebmeier 2012). While Arctic zooplankton do not consume the majority of the primary production nutrients, the newcomers do, leaving less carbon available for the benthos region (Grebmeier 2012). This may be causing a decrease in major groups of benthic fauna such as bivalves, amphipods, polychaetes, and sipunculids, which in turn affects species’ population density and growth rates up trophic levels, including the Pacific walrus, California gray whale, and spectacled eider. Correspondingly, pelagic organisms may begin to increase in number (Grebmeier 2012). Continual monitoring and additional studies are being conducted by several organizations to keep track of the changing nature of Arctic marine ecosystems.-Katherine Recinos

Grebmeier, Jacqueline M., 2012. Shifting Patterns of Life in the Pacific Arctic and Sub-Arctic Seas. Annual Review of Marine Science 4, 63–78.

Jacqueline Grebmeier used data from a series of other studies to illustrate the changes taking place in Pacific Arctic and Sub-Arctic. The formation and melting of sea ice is intricately connected with seasonal phytoplankton blooms and chlorophyll a levels. Phytoplankton blooms begin as the sea ice starts to melt. There are two opposing theories on the effects of earlier ice degradation caused by global warmer. The first is that lack of corresponding sunlight will inhibit phytoplankton blooming. The second hypothesizes that the additional time gained will allow for increased phytoplankton blooming. Data may prove the second to be true. Increased primary production and warmer water temperatures are fueling the migration of larger Pacific zooplankton to northern Arctic regions. This is changing the ecosystem there as the new zooplankton consume more nutrients so fewer nutrients make their way to the benthos from the pelagic . Also, the species composition of pelagic zooplankton will differ because the new zooplankton cannot survive Arctic winter temperatures.

Grebmeier goes on to demonstrate the lack of nutrients in the benthic by citing studies on sediment community oxygen consumption which show carbon usage in the benthos. Because the area in question is “benthic-dominated,” reduced benthic nutrient supplies will negatively impact populations of key benthic species such as those mentioned above. These species are the main food source for larger marine predators. Grebmeier presents the example of bivalves in the northern Bering Sea. Spectacled eiders, a type of sea diving duck, feed on them. A decrease in bivalves has led to an observed decrease in spectacled eiders. “Clustered community” interactions are common in the Pacific Arctic and Sub-Arctic so direct effects such as this would significantly affect species populations, growth rates, and ecosystems.

Grebmeier stresses the effects that changes in species populations and distribution could have on higher trophic levels. Walruses, gray whales, and other species are beginning to exhibit different behaviors to cope with environmental changes. Fish and invertebrates native to further south in the Pacific are also being observed in the Arctic and Sub-Arctic regions. This could stimulate the same type of competition between native and non native species seen in zooplankton population.

Grebmeier concludes by mentioning several initiatives including the Circumpolar Biodiversity Monitoring Program (CBMP) and the Pacific Arctic Group’s Distributed Biological Observatory (DBO), that are monitoring Arctic ecosystems. Specific location studies at stations and transects are especially useful methods. International cooperation is necessary for effective study and preservation.