1. Funding by COPAS Sur-Austral PFB-31, CONICYT Chile
Organic carbon in glacial fjords of Chilean Patagonia. S Pantoja1, MH Gutiérrez1, F Tapia1, L Abarzúa1, G Daneri1,2, B Reid2, B Díez3
1. Department of Oceanography and COPAS Sur-Austral, University of Concepción, Concepción, Chile
2. Center for Patagonian Ecosystem Research, Coyhaique, Chile
3. Department of Molecular Genetics and Microbiology, Pontifical Catholic University of Chile and Center for Climate and Resilience Research (CR)2, Santiago, Chile
halocline
0.2% C-org
<1% PP
Winter mixing
Gulf of Penas
120m
>200m
sediment
Open ocean
30m
100 km
120 km
halocline
0.2% C-org
<1% PP
Gulf of Penas
120m
>200m
sediment
Open ocean
30m
100 km
120 km
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Hypothesis: freshwater-ocean interaction determines hydrographic structure and productivity patterns
Spring-Summer
Autumn-Winter
Rates of surface marine primary production and community respiration indicate trend to heterotrophic ecosystem (Q=GPP-R <0)
Coastal Ocean in Chilean Patagonia receives continental freshwater with fluxes of ca. 30,000 m3 s-1 (Dávila et al. 2002, Cont Shelf Res 22, ).
Strong seasonality in both thermal structure and river discharge
Wintertime intrusions of near-bottom warm (oceanic) waters
Climatological means of SSS [psu]. Aquarius satellite (August 2011-June 2015)
•Warmer waters reaching the fjord’s head in winter are manifestation of fjord-scale ocean intrusions
•Vertical scale of mixing in the fjord should be maximal during winter, given the cooling of surface waters, minimal inputs of freshwater, and intense wind forcing.
•During summer the mixed layer should be at its thinnest, given strong stratification resulting from high freshwater discharges and solar warming of surface layers.
•This seasonal pattern in stratification and vertical mixing make it feasible that the oxygen content of waters found below a certain depth at the fjord’s head has been declining since wintertime intrusion.
•Hydrographic sections conducted along the fjord in spring and summer show depletion of oxygen that increased with depth and towards the fjord’s head. A strikingly similar pattern is observed for nitrate concentration.
•This pattern could result from remineralization of river-borne organic matter in the inner sections of the fjord.
Study area
Theoretical ratio NO3-/O2 = 0.12, based on Redfield stoichiometry (CH2O)106(NH3)16(H3PO4) +138O2  106CO2+ 16NO3 +H2PO4 +122H2O. Relationship between nitrate and oxygen vs. depth in Channels Martínez and Baker reveals a ratio NO3-/O2 near -0.2 (closed symbols indicate significant (a=0.05) correlation slope. Vertical lines correspond to r=0 and slope=0.11).
General circulation (Silva & Vargas 2014 Prog Oceanogr 129, 62-82) and estuarine-type circulation (C. Moffat)
Lack of mixing line of dissolved and particulate organic carbon may indicate that local marine production than a riverine or glacial source (end-member are not yet well-constrained).
Funding by COPAS Sur-Austral PFB-31, CONICYT Chile