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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.

Maiti, K, Charette MA, Buesseler KO, Kahru M.  2013.  An inverse relationship between production and export efficiency in the Southern Ocean. Geophysical Research Letters. 40:1557-1561.   10.1002/grl.50219   AbstractWebsite

In the past two decades, a number of studies have been carried out in the Southern Ocean to look at export production using drifting sediment traps and thorium-234 based measurements, which allows us to reexamine the validity of using the existing relationships between production, export efficiency, and temperature to derive satellite-based carbon export estimates in this region. Comparisons of in situ export rates with modeled rates indicate a two to fourfold overestimation of export production by existing models. Comprehensive analysis of in situ data indicates two major reasons for this difference: (i) in situ data indicate a trend of decreasing export efficiency with increasing production which is contrary to existing export models and (ii) the export efficiencies appear to be less sensitive to temperature in this region compared to the global estimates used in the existing models. The most important implication of these observations is that the simplest models of export, which predict increase in carbon flux with increasing surface productivity, may require additional parameters, different weighing of existing parameters, or separate algorithms for different oceanic regimes.

Anderson, CR, Kudela RM, Kahru M, Chao Y, Rosenfeld LK, Bahr FL, Anderson DM, Norris TA.  2016.  Initial skill assessment of the California Harmful Algae Risk Mapping (C-HARM) system. Harmful Algae. 59:1-18.   10.1016/j.hal.2016.08.006   AbstractWebsite

Toxic algal events are an annual burden on aquaculture and coastal ecosystems of California. The threat of domoic acid (DA) toxicity to human and wildlife health is the dominant harmful algal bloom (HAB) concern for the region, leading to a strong focus on prediction and mitigation of these blooms and their toxic effects. This paper describes the initial development of the California Harmful Algae Risk Mapping (C-HARM) system that predicts the spatial likelihood of blooms and dangerous levels of DA using a unique blend of numerical models, ecological forecast models of the target group, Pseudo-nitzschia, and satellite ocean color imagery. Data interpolating empirical orthogonal functions (DINEOF) are applied to ocean color imagery to fill in missing data and then used in a multivariate mode with other modeled variables to forecast biogeochemical parameters. Daily predictions (nowcast and forecast maps) are run routinely at the Central and Northern California Ocean Observing System (CeNCOOS) and posted on its public website. Skill assessment of model output for the nowcast data is restricted to nearshore pixels that overlap with routine pier monitoring of HABs in California from 2014 to 2015. Model lead times are best correlated with DA measured with solid phase adsorption toxin tracking (SPATI') and marine mammal strandings from DA toxicosis, suggesting long-term benefits of the HAB predictions to decision making. Over the next three years, the C-HARM application system will be incorporated into the NOAA operational HAB forecasting system and HAB Bulletin. (C) 2016 Elsevier B.V. All rights reserved.

Kahru, M, Mitchell BG.  2002.  Influence of the El Nino-La Nina cycle on satellite-derived primary production in the California Current. Geophysical Research Letters. 29   10.1029/2002gl014963   AbstractWebsite

[1] Time series of phytoplankton net primary production (NPP) for the California Current were derived using satellite data and the VGPM primary productivity model for a 5-year period (1997-2001) including the 1997-98 El Nino. NPP had a strong annual periodicity correlated with the El Nino-La Nina cycle. The most obvious effects of the El Nino on NPP were 100-300 km off the coast: a reduction by 30% off Southern California but an increase by 40% off Baja California. During its peak El Nino decreased NPP by 10-15% (1.5 Tg C month(-1)) in the 1000-km band off Southern California but increased by 20-30% off Northern and Southern Baja (4 Tg C month(-1)). The total annual NPP was lowest during the El Nino years of 1997-1998 and peaked in 2000. Trends of increasing NPP and zooplankton volume were observed off Central and Southern California.

Kahru, M, Mitchell BG.  2000.  Influence of the 1997-98 El Nino on the surface chlorophyll in the California Current. Geophysical Research Letters. 27:2937-2940.   10.1029/2000gl011486   AbstractWebsite

Satellite-derived time series for the California Current System (CCS) showed marked changes in the surface chlorophyll a concentration (Chl, mg m(-3)) associated with the 1997-98 El Nino. In addition to the previously known de crease in Chi off Southern California (Fiedler, 1984), we also observed a significant increase of Chi off Baja California. Whereas the extent of eutrophic (Chl > 1.0) areas decreased throughout the CCS, the extent of mesotrophic areas (0.2 < Chi < 1.0) off Baja California approximately doubled. The reduced area of eutrophic waters is attributed to weakened upwelling but the increase in the offshore mesotrophic area off Baja may be caused by blooms of nitrogen-fixing cyanobacteria. Using revised Coastal Zone Color Scanner data we detected similar changes during the 1982-83 El Nino.

Kahru, M.  1982.  The influence of hydrodynamics on the chlorophyll field in the open Baltic. Hydrodynamics of semi-enclosed seas : proceedings of the 13th International Liege Colloquium on Ocean Hydrodynamics. ( Nihoul JCJ, Ed.).:531-541.: Elsevier Scientific Pub. Co. Abstract
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Manzano-Sarabia, M, Salinas-Zavala CA, Kahru M, Lluch-Cota SE, Gonzalez-Becerril A.  2008.  The impact of the 1997-1999 warm-SST and low-productivity episode on fisheries in the southwestern Gulf of Mexico. Hydrobiologia. 610:257-267.   10.1007/s10750-008-9440-y   AbstractWebsite

Satellite-derived time-series of sea surface temperature (SST), chlorophyll a, and net primary productivity showed a period of warm SST and low productivity during 1997 and 1999 in the southwestern Gulf of Mexico followed by a period of colder than average SST (2000-2001). This shift between the warm and cold oceanic conditions might have caused significant changes in the structure of the ecosystem that is shown by changes in primary productivity and fishery landings between those periods.