Seasonal variation of colored dissolved organic matter in the Nelson Estuary, Hudson Bay

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1 Seasonal variation of colored dissolved organic matter in the Nelson Estuary, Hudson Bay C. Guéguen 1, A. Perroud 1, G. McCullough 2, D. G. Barber 2 1 Department of Chemistry, Trent University 2 Centre for Earth Observation Science, University of Manitoba

2 Dissolved organic matter (DOM) in the upper layers constitutes a large carbon pool in the Ocean, but little is known about its dynamics, i.e., production mechanisms, distribution and composition. General aspects of DOM dynamics in the upper layers Controls by terrestrial inputs, in situ activity and photochemical processes Major fractions are molecularly-uncharacterized uncharacterized components For a better understanding of DOM dynamics Sample intensive studies (e.g., optical properties) Lower structural detail High sample throughput Advanced technique approaches (e.g. NMR, FlFFF) Better structure details Low sample throughput

Optical Properties of Colored Dissolved Organic Matter (CDOM) DOC [um-c] CDOM [AU] 0 0 20

3 Optical Properties of Colored Dissolved Organic Matter (CDOM) DOC [um-c] CDOM [AU] pcdom tcdom Depth [m] DOC vs Col Depth [m] Method: Absorbance and fluorescence spectroscopies on GFF filtered surface waters collected in 2007, 2009 and 2010

4 Hudson Bay Hudson Bay receives > 1/3 of Canada s freshwater drainage Source: Straneo and Saucier (2008)

5 Hudson Bay Water Inventories Nelson R. Arrows symbolize river runoff Modified from Granskog et al. (2011)

6 Manitoba Hydro s Churchill River diversion Source: Manitoba Hydro

7 Optical Properties of CDOM in Objectives Hudson Bay 1. Optical properties = proxies of DOC in HB? 2. Spatial dynamics of DOM 3. Estuarine processes affecting DOM optical properties courtesy of NASA/GSFC, MODIS Rapid Response

8 Methods 3 cruises in 2007, 2009 and 2010 on the CCGS Amundsen 191 samples GFF filtered surface waters DOM characterization DOC Optical properties : absorbance and EEM

9 PARAFAC PARAFAC statistically decompose EEMs into independent fluorescent group C1 = Terrestrial Observed EEM Modeled EEM C2 = Microbial C3 = Protein-like

10 DOM composition Conservative behavior of DOM in HB estuaries (S<23) Higher [DOC] and [CDOM] in rivers than in open waters DOC [um-c] Salinity Guéguen et al. (2011) a355 [m-1] Hudson Strait Nelson R. Great Whale R Salinity

11 DOM composition a355 and fluorescence = proxies of DOC in NR estuary non-absorbing DOC non-fluorescing DOC 16 [%] [%] Summer ± 3 32 ± 9 Summer ± 8 44 ± Winter ± 5 20 ± 17 a355 [m-1] DOC [ppm-c] Summer2010 Summer2007 Winter2009

12 Strait DOM composition NE SW Nelson/Hayes R. SE James Component Intensity [r.u.] Hudson Strait NE Hudson Bay SE Hudson Bay James Bay SW Hudson Bay C1 C2 C3 Terrestrial microbial protein-like Guéguen et al. (2011)

13 Nelson River estuary Nelson River = 1/3 of HB freshwater 100-m Nelson R.

14 Fluorescence Indices High HIX + low BIX = dominance of allochthonous DOM Similar indices in summer = similar origin and nature of DOM Microbial Humified Autochthonous Terrestrial Fresh Allochthonous Summer2010 Summer2007 Summer2009 Winter 2009

15 Temporal changes in the coastal region lower salinity higher DOC and a 355 higher terrestrial DOM % Nelson R offshore Summer2010 Summer2007 Summer2009

16 PARAFAC-PCA PCA More saline and less humified due to low river flow in 2010 PC2 loadings (22.1%) %C3 BIX Salinity S Fl Protein-like %C1 a355 PC Salinity -0.6 %C2 HIX PC1 loadings (51.5%) PC Humified terrestrial DOM

18 PARAFAC-PCA PCA No significant impact of tidal stage limited offshore mixing %C3 Fl 4 Protein-like DOM PC2 loadings (22.1%) %C1 BIX a355 Salinity Flood ebb S %C2 HIX PC1 loadings (51.5%) PC Flood current Ebb current PC1 Humified terrestrial DOM

19 Seasonal exchange Coastal circulation Coastal domain: variable DOM composition and concentration Interior domain: constant DOM composition and concentration

20 Conclusions Conservative mixing of a355 and fluorescent DOM Optical properties = good proxies in HB Significant difference in DOM composition HS waters less humified than HB waters Temporal variation in estuarine mixing River waters limited to coastal domain limited exchange with interior domain

21 Questions? Acknowledgment Canada Research Chairs

HUDSON BAY OPTICS. A synthesis of current knowledge with a view towards the future. Pierre Larouche, InsDtut Maurice- Lamontagne

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