Publications

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2018
Kahru, M, Jacox MG, Ohman MD.  2018.  CCE1: Decrease in the frequency of oceanic fronts and surface chlorophyll concentration in the California Current System during the 2014-2016 northeast Pacific warm anomalies. Deep-Sea Research Part I-Oceanographic Research Papers. 140:4-13.   10.1016/j.dsr.2018.04.007   AbstractWebsite

Oceanic fronts are sites of increased vertical exchange that are often associated with increased primary productivity, downward flux of organic carbon, and aggregation of plankton and higher trophic levels. Given the influence of fronts on the functioning of marine ecosystems, an improved understanding of the spatial and temporal variability of frontal activity is desirable. Here, we document changes in the frequency of sea-surface fronts and the surface concentration of chlorophyll-a (Chla) in the California Current System that occurred during the Northeast Pacific anomalous warming of 2014-2015 and El Nino of 2015-2016, and place those anomalies in the context of two decades of variability. Frontal frequency was detected with the automated histogram method using datasets of sea-surface temperature (SST) and Chla from multiple satellite sensors. During the anomalous 2014-2016 period, a drop in the frequency of fronts coincided with the largest negative Chla anomalies and positive SST anomalies in the whole period of satellite observations (1997-2017 for Chla and 1982-2017 for SST). These recent reductions in frontal frequency ran counter to a previously reported increasing trend, though it remains to be seen if they represent brief interruptions in that trend or a reversal that will persist going forward.

2015
Jacox, MG, Edwards CA, Kahru M, Rudnick DL, Kudela RM.  2015.  The potential for improving remote primary productivity estimates through subsurface chlorophyll and irradiance measurement. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 112:107-116.   10.1016/j.dsr2.2013.12.008   AbstractWebsite

A 26-year record of depth integrated primary productivity (PP) in the Southern California Current System (SCCS) is analyzed with the goal of improving satellite net primary productivity (PP) estimates. Modest improvements in PP model performance are achieved by tuning existing algorithms for the SCCS, particularly by parameterizing carbon fixation rate in the vertically generalized production model as a function of surface chlorophyll concentration and distance from shore. Much larger improvements are enabled by improving the accuracy of subsurface chlorophyll and light profiles. In a simple vertically resolved production model for the SCCS (VRPM-SC), substitution of in situ surface data for remote sensing estimates offers only marginal improvements in model r(2) (from 0.54 to 0.56) and total log(10) root mean squared difference (from 0.22 to 0.21), while inclusion of in situ chlorophyll and light profiles improves these metrics to 0.77 and 0.15, respectively. Autonomous underwater gliders, capable of measuring subsurface properties on long-term, long-range deployments, significantly improve PP model fidelity in the SCCS. We suggest their use (and that of other autonomous profilers such as Argo floats) in conjunction with satellites as a way forward for large-scale improvements in PP estimation. (C) 2013 Elsevier Ltd. All rights reserved.