Conclusions
Acknowledgements
I would like to thank Kristin Hänselmann and Erika Allhusen for their help during the sampling; Ellen Damm, Elisabeth Helmke and Gerhard Dieckmann for fruitful discussions; the AWI-Sea Ice Physics group for all their work and all the participants and crew
members of the RV Polarstern ARK XXVI/3 Expedition 2011.
Reference
Gosselin M, Levasseur M, Wheeler M, Horner RA & Booth BC. (1998) New measurements of phytoplankton and ice algal production in the Arctic Ocean. Deep-Sea Research. 44(8).
Sea Ice Primary Productivity in the Central Arctic Ocean during summer 2011
Mar Fernández Méndez
1*,2, Ilka Peeken
1, Eva-Maria Nöthig
1, Frank Wenzhöfer
1,2and Antje Boetius
1,2HGF-MPG Group for Deep Sea Ecology and Technology
1Alfred Wegener Institute for Polar and Marine Reseach , Bremerhaven, Germany
2Max Planck Institute for Marine Microbiology, Bremen, Germany Mar.Fernandez.Mendez@awi.de*
Introduction
.
Results
Figure 1. Cruise track (blue line) and ice
stations (red dots) (M. Nicolaus).
Nutrient provinces (boxes) defined by the differences in
Phosphate (P) and Nitrate (N)
concentrations (- stands for depleted) (E. Damm).
Methods
Radioactive isotope 14C-Method
1. 24 h Incubation (10 µE/m2 s; Light, -2°C) 2. Filtration 0.2 µm poresize
3. Acidification 6M HCl
4. Liquid scintillation counting
Outlook
Water column Sea Ice Melt Ponds
Figure 2. Sampling methods: CTD rosette, ice corer and vacuum pump.
Arctic sea ice is a very dynamic environment which is currently suffering a rapid decline in extent and thickness. Besides the phyto- plankton in the surface waters, sea ice algae can contribute up to 57% to primary production (Gosselin et al 1997), but our knowledge about their activity, especially in the central basins, is still limited.
Surface Water Sea Ice Melt Ponds
0 2 4 6 8 10 12 14 16
201 205
207 209
212 214
216 218
220 221
222 223
225 226
227 228
229 230
233 235
239 240
242 245
247 248
250 252 Station
NPP (µg C/ L d)
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9
Chl a (µg/L)
NPP Chl a
0 50 100 150 200 250
203
209
212
218
222
227
230
235
239
245
250 Station
NPP (µg C / L d)
Top Middle Bottom
0 1 2 3 4 5 6
Chl a (µg / L)
Bottom Middle Top
0 50 100 150 200 250 300 350 400 450 500
203
209
212
218
222
227
235
239
245
250 Station
NPP (µg C/ L d)
0 5 10 15 20 25 30
Chl a (µg/L)
NPP Chl a
Figure 3. Net primary productivity rates and chlorophyll a concentrations in surface water samples (2-5 m depth) from Atlantic to Pacific influenced waters. First stations correspond to early August and the last ones to late September 2011.
Figure 4. Net primary productivity rates and chlorophyll a concentrations of ice cores melted in filtered sea water divided in top, middle and bottom part. Note that in stations 203 and 209, top and middle were not measured.
Figure 5. Net primary productivity rates and chlorophyll a concentrations of all melt ponds sampled during TransArc. Picture a shows aggregates found in open melt ponds at station 212. Picture b shows an example of refrozen melt pond covered by snow. Note that refreezing started in early september (station 218).
Figure 6. Relative contribution to NPP; Chl a normalized rates of the different habitats considering just surface waters, sea ice and melt ponds.
Sea Ice hosts the most active autotrophs under low light conditions. Nevertheless, when compared to the integrated water column its contribution to the arctic carbon cycle during summer is one order of magnitude lower compared to the water column.
Melt Pond aggregates sustain the highest productivity rates of all before the re- freezing starts.
Surface waters from the Atlantic influenced region show high phytoplankton biomass standing stocks but low productivity, while the other regions are characterized by generally low NPP rates compared to sea ice and melt ponds.
• Unravel the limiting factors for primary productivity in sea ice and surface waters by nutrient bioassays and photosynthesis-irradiance curves.
• Upscale primary productivity to the entire Arctic Ocean.
• Reveal the key groups responsible for carbon fixation in each habitat.
• Determine the carbon transfer rates from melt pond algae to bacteria.
Aggregates (~10 cm)
Multi Year Ice
Mixed waters -P -N
Pacific waters +P -N
Mixed waters +P +N
Atlantic waters -P +N
During the Polarstern summer expedition TransArc 2011 to the Central Arctic, potential Net Primary Productivity rates (NPP) and Chlorophyll a were measured in different habitats: surface waters, sea ice and melt ponds; to assess the importance of sea ice algae carbon fixation and biomass compared to phytoplankton and melt pond autotrophs.
Refrozen-snow covered
a
b
NPP (mg C*m-2*d-1)
Water mixed layer Sea Ice
Figure 7. Integrated NPP rates for the euphotic zone assuming similar photosynthetic activity throughout the mixed layer (Mixed Layer Depth: 10 to 50 m) and for the sea ice (Sea Ice thickness: 1 to 3 m). Note that the scales differ by one order of magnitude.
0-600 mg C*m-2*d-1 2-17 mg C*m-2*d-1
7000 (µg C/L d) 170 (µg Chl a/L)
% NPP (µg C*µg Chl a-1*d-1)
0% 20% 40% 60% 80% 100%
212 222 227 235 239 245 250
Station
Surface waters Sea Ice
Melt Ponds
0 50 100 150 200 250
Surface Water
Sea Ice Melt Ponds
NPP (µg C* µg Chl a-1 * d-1 )
