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pH tipping point in Svalbard (pHinS)
IADC_id: 47
active
Call year: 2016
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Relative to seawater, unexpectedly high pH values can be found in Kongsfjorden, west Svalbard. Within the fjord, surface water pH reached up to 8.6 in summer 2015. As the fjord is open (with no sill to restrict circulation) and fjord circulation generally removes meltwater quickly, the mean pH of freshwater inputs from both land and marine terminating glaciers discharging into the fjord must be very alkaline in order to maintain such a high pH. Glacial meltwater feeding into the fjord from a large land terminating glacier is known to have high pH (up to 10), but it is not clear whether this is representative of inputs from groundwater or sub-glacial drainage.rnIncreasing air temperatures in the Arctic are likely to increase annual discharge and glacial retreat in the coming decades. In the longer term meltwater discharge must ultimately decline if the present negative ice sheet mass balance is maintained. If glacial inputs are important for maintaining a high pH in fjord waters, a pH tipping point will then theoretically be reached as meltwater inputs to the fjord decrease. This should result in a rapid decline in fjord pH towards values more representative of coastal systems (8.0, or lower in a future higher CO2 world). This rapid pH decline has the potential to be among the fastest natural changes ever reported for a natural body of oxygenated seawat. Kongsfjorden is therefore a very interesting natural laboratory in which the ecosystem response to this pH change could be easily be monitored due to the presence of the Ny-Alesund research station.rnThe primary driver of very high pH in meltwater is normally the hydrolysis of carbonate and silicate mineral phases. These reactions only occur with freshly deposited glacial flour (fine ground rock), so the ability of a glaciated system to drive high pH downstream depends on the active production of fresh glacial flour. Prolonged glacial retreat may, in the short term, expose large quantities of glacial flour and thus supply ample material to maintain high pH in all water draining through the pro-glacial moraine, but carbonate and silicate phases will, ultimately, be depleted such that the pH of water draining through a freshly de-glaciated catchment will no longer be driven to high pH. Changing sediment loads should also directly affect alkalinity and pCO2 as reactive sediment phases increase alkalinity and decrease pCO2 in meltwater, which is normally undersaturated with respect to atmospheric pCO2.rnIn addition to diluting seawater with low salinity and low alkalinity meltwater, glaciers can drive the local circulation of fjords. Subglacial meltwater discharge typically causes localized upwelling close to marine terminating glacial fronts. This brings deep seawater to the surface and drives primary production, which in turn stimulates CO2 drawdown. Determining the effect of changing glacial meltwater fluxes and glacial retreat on coastal pH values is therefore very difficult as several physical and biological features of glacial systems act concurrently in affecting pH values in adjacent waters.rnAs increasing annual air temperatures and glacial retreat are well established phenomena across much of the Arctic, we expect that pH in the fjords around Spitsbergen may be subject to pronounced pH changes in the near future due to changing meltwater fluxes. Longer and warmer meltwater seasons may increase glacial meltwater fluxes around Svalbard in the near (decades) future, but these fluxes must eventually be subject to a decline due to the negative mass balance of the Svalbard Ice Sheets. A short-term increase in the input of alkaline freshwater into adjacent fjords will, we hypothesize, be followed by a longer-term decline. Given the ongoing increase in atmospheric pCO2 due to anthropogenic emissions, this will, presumably, be accompanied by a sharp decrease in fjord seawater pH.rnIn addition to high pH arising in some meltwater streams around Spitsbergen, fieldwork carried out in summer 2015, identified several locations where very acidic seepages entered meltwater streams. The mechanism driving formation of these acidic seepages around Svalbard has not yet been reported, and similarly the volume of such seepages has not been calculated. Whilst they are a minor feature compared to other freshwater dischargers, the weathering that drives their formation may increase with increasing summer temperatures. Furthermore, if they persist in de-glaciated catchments, the decline in freshwater pH once glacial flour supply is exhausted may be even more drastic. In addition to affecting pH, a change from alkaline meltwater supply to slightly acidic freshwater supply will have consequences for the delivery of trace metal nutrients to fjord ecosystems.rnThe overarching aim of this work will be to construct the first forecast of how pH will change in Kongsfjorden in the next decades. To do this a simple model will be constructed, largely using existing hydrological data, which quantifies water mass movements in Kongsfjorden throughout the year. By combining this with the measurements of the carbonate system, air-sea CO2 fluxes and the other data gathered during the proposed fieldwork, we will be able to provide a first estimate of how changes to this system will affect pH.rnMilestones:rn1. Measuring the composition (dissolved inorganic carbon - DIC, alkalinity, pH, dissolved organic carbon - DOC, nutrients) of the different freshwater inputs into the fjord (runoff, sub-glacial meltwater, calved ice, ground water, precipitation) and in coastal seawater.rn2. Constructing a simple box model of freshwater movements into the fjord using existing knowledge of hydrological inputs, physical circulation and our own CTD casts to establish the approximate present boundaries of different hydrological zones in summer.rn3. Estimating how freshwater inputs change seasonally and inter-annually using all available hydrological data and, by involving a UNIS (The University Centre In Svalbard) partner, quantifying how the carbonate system changes at an accessible glacial meltwater stream throughout at least one full meltwater season.rn4. Estimate how the fjord pH will change in the intermediate future and how anthropogenic pertubations to the climate will affect this change.rnFrameworkrnThe proposed work is an extension of the EU funded project ‘Ocean Certain’ http://oceancertain.eu/, where ISMAR-CNR and GEOMAR are consortium partners. rn
National/International Cooperation:
GEOMAR - Helmholtz Centre for Ocean Research Kiel, GermanyrnUNIS/NTNU - The University Centre in Svalbard / Norwegian University of Science and Technology, NorwayrnOCEAN CERTAIN - Ocean Food-web Patrol – Climate Effects: Reducing Targeted Uncertainties with an Interactive Network (FP7)rnGEOTRACES – An international study of the marine biogeochemical cycles of trace elements and their isotopes.rnrn
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