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Schwarz, JN, Kowalczuk P, Kaczmarek S, Cota GF, Mitchell BG, Kahru M, Chavez FP, Cunningham A, McKee D, Gege P, Kishino T, Phinney DA, Raine R.  2002.  Two models for absorption by coloured dissolved organic matter (CDOM). Oceanologia. 44:209-241. AbstractWebsite

The standard exponential model for CDOM absorption has been applied to data from diverse waters. Absorption at 440 nm (a(g)440) ranged between close to zero and 10 m(-1), and the slope of the semilogarithmic absorption spectrum over a minimum range of 400 to 440 nm (s440) ranged between < 0.01 and 0.04 nm(-1). NO relationship was found between a(g)440 or s440 and salinity. Except in the southern Baltic, s440 was found to have abroad distribution (0.0165 +/- 0.0035), suggesting that it should be introduced as an additional variable in bio-optical models when a(g)440 is large. An alternative model for CDOM absorption was applied to available high quality UV-visible absorption spectra from the Wisla river (Poland). This model assumes that, the CDOM absorption spectrum comprises distinct Gaussian absorption bands in the UV, similar to those of benzene. Five bands were fit to the data. The mean central energy of all hands was higher in early summer (E &SIM;7.2, 6.6, 6.4, 6.2 and 5.5 eV or 172, 188, 194, 200 and 226 nm)) than in winter. The higher energy bands were found to decay in both height and width with increasing salinity, while lower energy bands broadened with increasing salinity. 8440 was found to be correlated with shape parameters of the bands centred at 6.4 and 5.5 eV. While the exponential model is convenient for optical modelling and remote sensing applications, these results suggest that the Gaussian model offers a deeper understanding of chemical interactions affecting CDOM molecular structure.

Kahru, M, Kudela RM, Manzano-Sarabia M, Mitchell BG.  2012.  Trends in the surface chlorophyll of the California Current: Merging data from multiple ocean color satellites. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 77-80:89-98. Abstract

Standard remote sensing reflectance products from four ocean color sensors (OCTS, SeaWiFS, MODISA, MERIS) and over 10,000 in situ measurements of surface chlorophyll-a (Chl-a) concentration in the California Current were used to create empirical algorithms that are consistent with in situ data as well as between individual sensors. Using these algorithms, a merged multi-sensor time series of the surface Chl-a concentration in California Current region was created. The merged Oil-a time series (November 1996-December 2011) show a significant (P < 0.01) increasing trend off central California and significant (P < 0.01) decreasing trends in the central North Pacific gyre and off southern Baja California. Although this 15-year time series is too short to separate interannual and multidecadal cycles from climate trends, both of these trends are consistent with the predicted effects of global warming. The expected increase in vertical stratification of the water column and the resulting decreased vertical flux of nutrients would lead to lower Chl-a in the gyre but the increased upwelling-favorable winds leading to stronger upwelling off central California or the increased nitrate content of the upwelled water would lead to higher Chl-a in the upwelling region. The decreased Chl-a off southern Baja California resembles the effect of a decreased influence of strong El Nino events. (c) 2012 Elsevier Ltd. All rights reserved.

Kahru, M, Kudela R, Manzano-Sarabia M, Mitchell BG.  2009.  Trends in primary production in the California Current detected with satellite data. Journal of Geophysical Research-Oceans. 114   10.1029/2008jc004979   AbstractWebsite

Several ocean primary production algorithms using satellite data were evaluated on a large archive of net primary production (NPP) and chlorophyll-a (Chl-a) measurements collected by the California Cooperative Fisheries Investigations program in the California Current. The best algorithm matching in situ data was found by empirically adjusting the Behrenfeld-Falkowski Vertically Generalized Production Model. Satellite-derived time series of NPP were calculated for the California Current area. Significant increase in NPP and Chl-a annual peak levels, i.e., the "bloom magnitude,'' were found along the coasts of the California Current as well as other major eastern boundary currents for the period of modern ocean color data (1997-2007). The reasons for this increase are not clear but are associated with various environmental conditions.

Smith, KL, Ruhl HA, Kaufmann RS, Kahru M.  2008.  Tracing abyssal food supply back to upper-ocean processes over a 17-year time series in the northeast Pacific. Limnology and Oceanography. 53:2655-2667.   10.4319/lo.2008.53.6.2655   AbstractWebsite

Detrital aggregates episodically deposited on the seafloor represent an underestimated food source to deep-sea communities. A 17-yr time-series study was conducted from 1990 to 2006 in the abyssal northeast Pacific (Sta. M, 4100 m in depth) to evaluate the importance of this food source and its temporal relationship to water column and surface ocean processes. Detrital aggregates appeared on the seafloor from June through December, with the highest peaks in 1990, 1994, 2001, and 2002 reaching a maximum density of 23 m(-2) in fall 2001. A total of 15,816 aggregates were measured, most less than 20 cm(2) in area and with a mode of 9 cm(2). Density of detrital aggregates was highly correlated with particulate organic carbon (POC) flux at 600 and 50 m above the bottom (p < 0.001) with no time lag. Export flux of organic carbon from the euphotic zone was significantly correlated with aggregate density, lagged earlier by 1-4 months (p <= 0.001). Zooplankton displacement volume was significantly correlated with POC flux (p =0.023) and with detrital aggregate density (p =0.028) on the seafloor when lagged earlier by <= 1 month. The Bakun upwelling index computed for the region around Sta. M was significantly correlated with detrital aggregate density when lagged earlier by 2-5 months (p < 0.001). A strong correlation exists between surface ocean processes and abyssal food supply, including POC flux and detrital aggregates. This direct coupling through the entire water column must be considered in resolving the marine carbon cycle.

Holm-Hansen, O, Kahru M, Hewes CD, Kawaguchi S, Kameda T, Sushin VA, Krasovski I, Priddle J, Korb R, Hewitt RP, Mitchell BG.  2004.  Temporal and spatial distribution of chlorophyll-a in surface waters of the Scotia Sea as determined by both shipboard measurements and satellite data. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 51:1323-1331.   10.1016/j.dsr2.2004.06.004   AbstractWebsite

Chlorophyll-a (Chl-a) concentrations in surface waters were measured at 137 hydrographic stations occupied by four research vessels participating in the CCAMLR 2000 Survey and the values were compared to estimates from data acquired by the SeaWiFS satellite. The Chl-a concentrations measured on board ship ranged from 0.06 to 14.6 mg m(-3), a range that includes most surface Chl-a concentrations during mid-summer in the Southern Ocean. Owing to persistent cloud cover over much of the Southern Ocean, it was necessary to acquire multi-day composites of satellite data in order to obtain reliable estimates of Chl-a at each of the hydrographic stations. The correlation between the median value for the eight-day composites and the Chl-a concentrations measured on board ship had an R-2 value of 0.82, with the satellite data under-estimating the values obtained on board ship at high Chl-a concentrations and slightly overestimating the shipboard data at Chl-a concentrations of < 0.2 mg m(-3). For Chl-a concentrations of < 1.0 mg m(-3), the ratio of the satellite estimates divided by the shipboard values was 0.89 +/- 0.45 (n = 50). As the mean Chl-a concentration in most pelagic Antarctic waters is close to 0.5 mg m(-3), satellite estimates for Chl-a concentrations in surface waters are thus close to shipboard measurements, and offer the advantage of providing synoptic maps of Chl-a distribution over extensive areas of the Southern Ocean. Satellite Chl-a images for the months preceding (December 1999) and following (February 2000) the CCAMLR 2000 Survey cruises showed that the general pattern of Chl-a concentration in the Scotia Sea and adjoining waters was similar in all three months, but that the phytoplankton biomass was generally lowest in December, reached maximal values in January, and started to decline in February. in contrast, Chl-a concentrations in Drake Passage declined progressively from early December through February. Published by Elsevier Ltd.