Publications

Export 4 results:
Sort by: Author Title Type [ Year  (Desc)]
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.

2014
Kahru, M, Kudela RM, Anderson CR, Manzano-Sarabia M, Mitchell BG.  2014.  Evaluation of satellite retrievals of ocean chlorophyll-a in the California Current. Remote Sensing. 6:8524-8540.   10.3390/rs6098524   AbstractWebsite

Retrievals of ocean surface chlorophyll-a concentration (Chla) by multiple ocean color satellite sensors (SeaWiFS, MODIS-Terra, MODIS-Aqua, MERIS, VIIRS) using standard algorithms were evaluated in the California Current using a large archive of in situ measurements. Over the full range of in situ Chla, all sensors produced a coefficient of determination (R-2) between 0.79 and 0.88 and a median absolute percent error (MdAPE) between 21% and 27%. However, at in situ Chla > 1 mg m(-3), only products from MERIS (both the ESA produced algal_1 and NASA produced chlor_a) maintained reasonable accuracy (R-2 from 0.74 to 0.52 and MdAPE from 23% to 31%, respectively), while the other sensors had R-2 below 0.5 and MdAPE higher than 36%. We show that the low accuracy at medium and high Chla is caused by the poor retrieval of remote sensing reflectance.

2013
Smith, KL, Ruhl HA, Kahru M, Huffard CL, Sherman AD.  2013.  Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean. Proceedings of the National Academy of Sciences of the United States of America. 110:19838-19841.   10.1073/pnas.1315447110   AbstractWebsite

The deep ocean, covering a vast expanse of the globe, relies almost exclusively on a food supply originating from primary production in surface waters. With well-documented warming of oceanic surface waters and conflicting reports of increasing and decreasing primary production trends, questions persist about how such changes impact deep ocean communities. A 24-y time-series study of sinking particulate organic carbon (food) supply and its utilization by the benthic community was conducted in the abyssal northeast Pacific (similar to 4,000-m depth). Here we show that previous findings of food deficits are now punctuated by large episodic surpluses of particulate organic carbon reaching the sea floor, which meet utilization. Changing surface ocean conditions are translated to the deep ocean, where decadal peaks in supply, remineralization, and sequestration of organic carbon have broad implications for global carbon budget projections.

2011
McQuatters-Gollop, A, Reid PC, Edwards M, Burkill PH, Castellani C, Batten S, Gieskes W, Beare D, Bidigare RR, Head E, Johnson R, Kahru M, Koslow JA, Pena A.  2011.  Is there a decline in marine phytoplankton? Nature. 472:E6-E7.   10.1038/nature09950   AbstractWebsite

Phytoplankton account for approximately 50% of global primary production, form the trophic base of nearly all marine ecosystems, are fundamental in trophic energy transfer and have key roles in climate regulation, carbon sequestration and oxygen production. Boyce et al. compiled a chlorophyll index by combining in situ chlorophyll and Secchi disk depth measurements that spanned a more than 100-year time period and showed a decrease in marine phytoplankton biomass of approximately 1% of the global median per year over the past century. Eight decades of data on phytoplankton biomass collected in the North Atlantic by the Continuous Plankton Recorder (CPR) survey, however, show an increase in an index of chlorophyll (Phytoplankton Colour Index) in both the Northeast and Northwest Atlantic basinsFig. 1), and other long-term time series, including the Hawaii Ocean Time-series (HOT)8, the Bermuda Atlantic Time Series (BATS)8 and the California Cooperative Oceanic Fisheries Investigations (CalCOFI)9 also indicate increased phytoplankton biomass over the last 20–50 years. These findings, which were not discussed by Boyce et al.1, are not in accordance with their conclusions and illustrate the importance of using consistent observations when estimating long-term trends.