Publications

Export 20 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.

2017
Kahru, M, Lee ZP, Mitchell BG.  2017.  Contemporaneous disequilibrium of bio-optical properties in the Southern Ocean. Geophysical Research Letters. 44:2835-2842.   10.1002/2016gl072453   AbstractWebsite

Significant changes in satellite-detected net primary production (NPP, mgCm(-2)d(-1)) were observed in the Southern Ocean during 2011-2016: an increase in the Pacific sector and a decrease in the Atlantic sector. While no clear physical forcing was identified, we hypothesize that the changes in NPP were associated with changes in the phytoplankton community and reflected in the concomitant bio-optical properties. Satellite algorithms for chlorophyll a concentration (Chl a, mgm(-3)) use a combination of estimates of the remote sensing reflectance Rrs() that are statistically fitted to a global reference data set. In any particular region or point in space/time the estimate produced by the global mean algorithm can deviate from the true value. Reflectance anomaly (RA) is supposed to remove the first-order variability in Rrs() associated with Chl a and reveal bio-optical properties that are due to the composition of phytoplankton and associated materials. Time series of RA showed variability at multiple scales, including the life span of the sensor, multiyear and annual. Models of plankton functional types using estimated Chl a as input cannot be expected to correctly resolve regional and seasonal anomalies due to biases in the Chl a estimate that they are based on. While a statistical model using RA() time series can predict the times series of NPP with high accuracy (R-2=0.82) in both Pacific and Atlantic regions, the underlying mechanisms in terms of phytoplankton groups and the associated materials remain elusive.

2016
Martinez-Fuentes, LM, Gaxiola-Castro G, Gomez-Ocampo E, Kahru M.  2016.  Effects of interannual events (1997-2012) on the hydrography and phytoplankton biomass of Sebastian Vizcaino Bay. Ciencias Marinas. 42:81-97.   10.7773/cm.v42i2.2626   AbstractWebsite

Sebastian Vizcaino Bay (Baja California Peninsula, Mexico) presents hydrographic conditions and phytoplankton biomass corresponding to a temperate/subtropical transition zone affected by large-scale tropical and subtropical events and those events originating in the subpolar Pacific region. Conditions in the first 50 m depth of the bay are mostly temperate (average temperature: 15.5 degrees C; average salinity: 33.6) and mesotrophic (phytoplankton biomass: >1 mg m(-3)). During spring and summer the bay is heavily influenced by the water transported by the California Current and the coastal upwelling generated off Punta Canoas. During the rest of the year the hydrography and phytoplankton biomass are mostly associated with subtropical conditions. The ENSO events arising in the period 1997-2012 affected the bay's water column. The extreme 1997-1998 El Nino generated increases of similar to 8 degrees C in temperature and similar to 0.8 in salinity. Local dynamic processes decreased the effects of moderate and weak El Nino events on phytoplankton biomass, with possible changes in the plankton functional groups. Due to the mostly temperate environment of the bay, the moderate 1998-2000 and 2010-2011 La Nina events did not generate a substantial change in the hydrography and phytoplankton biomass. However, the abundant subarctic water inflow in the period 2002-2006 abruptly decreased salinity and led to increased stratification of the water column and a reduction in phytoplankton chlorophyll.

2015
Kahru, M, Kudela RM, Anderson CR, Mitchell BG.  2015.  Optimized merger of ocean chlorophyll algorithms of MODIS-Aqua and VIIRS. Ieee Geoscience and Remote Sensing Letters. 12:2282-2285.   10.1109/lgrs.2015.2470250   AbstractWebsite

Standard ocean chlorophyll-a (Chla) products from currently operational satellite sensors Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Visible Infrared Imager Radiometer Suite (VIIRS) underestimate medium and high in situ Chla concentrations and have approximately 9% bias between each other in the California Current. By using the regional optimization approach of Kahru et al., we minimized the differences between satellite estimates and in situ match-ups as well as between estimates of the two satellite sensors and created improved empirical algorithms for both sensors. The regionally optimized Chla estimates from MODIS-Aqua and VIIRS have no bias between each other, have improved retrievals at medium to high in situ Chla, and can be merged to improve temporal frequency and spatial coverage and to extend the merged time series.

Kahru, M, Jacox MG, Lee Z, Kudela RM, Manzano-Sarabia M, Mitchell BG.  2015.  Optimized multi-satellite merger of primary production estimates in the California Current using inherent optical properties. Journal of Marine Systems. 147:94-102.   10.1016/j.jmarsys.2014.06.003   AbstractWebsite

Building a multi-decadal time series of large-scale estimates of net primary production (NPP) requires merging data from multiple ocean color satellites. The primary product of ocean color sensors is spectral remote sensing reflectance (Rrs). We found significant differences (13-18% median absolute percent error) between Rrs estimates at 443 nm of different satellite sensors. These differences in Rrs are transferred to inherent optical properties and further on to estimates of NPP. We estimated NPP for the California Current region from three ocean color sensors (SeaWiFS, MODIS-Aqua and MERIS) using a regionally optimized absorption based primary production model (Aph-PP) of Lee et al. (2011). Optimization of the Aph-PP model was required for each individual satellite sensor in order to make NPP estimates from different sensors compatible with each other. While the concept of Aph-PP has advantages over traditional chlorophyll-based NPP models, in practical application even the optimized Aph-PP model explained less than 60% of the total variance in NPP which is similar to other NPP algorithms. Uncertainties in satellite Rrs estimates as well as uncertainties in parameters representing phytoplankton depth distribution and physiology are likely to be limiting our current capability to accurately estimate NPP from space. Introducing a generic vertical profile for phytoplankton improved slightly the skill of the Aph-PP model. (C) 2014 Elsevier B.V. All rights reserved.

Saba, VS, Hyde KJW, Rebuck ND, Friedland KD, Hare JA, Kahru M, Fogarty MJ.  2015.  Physical associations to spring phytoplankton biomass interannual variability in the US Northeast Continental Shelf. Journal of Geophysical Research-Biogeosciences. 120:205-220.   10.1002/2014jg002770   AbstractWebsite

The continental shelf of the Northeast United States and Nova Scotia is a productive marine ecosystem that supports a robust biomass of living marine resources. Understanding marine ecosystem sensitivity to changes in the physical environment can start with the first-order response of phytoplankton (i.e., chlorophyll a), the base of the marine food web. However, the primary physical associations to the interannual variability of chlorophyll a in these waters are unclear. Here we used ocean color satellite measurements and identified the local and remote physical associations to interannual variability of spring surface chlorophyll a from 1998 to 2013. The highest interannual variability of chlorophyll a occurred in March and April on the northern flank of Georges Bank, the western Gulf of Maine, and Nantucket Shoals. Complex interactions between winter wind speed over the Shelf, local winter water levels, and the relative proportions of Atlantic versus Labrador Sea source waters entering the Gulf of Maine from the previous summer/fall were associated with the variability of March/April chlorophyll a in Georges Bank and the Gulf of Maine. Sea surface temperature and sea surface salinity were not robust correlates to spring chlorophyll a. Surface nitrate in the winter was not a robust correlate to chlorophyll a or the physical variables in every case suggesting that nitrate limitation may not be the primary constraint on the interannual variability of the spring bloom throughout all regions. Generalized linear models suggest that we can resolve 88% of March chlorophyll a interannual variability in Georges Bank using lagged physical data.

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.

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.

Kahru, M, Elmgren R.  2014.  Multidecadal time series of satellite-detected accumulations of cyanobacteria in the Baltic Sea. Biogeosciences. 11:3619-3633.   10.5194/bg-11-3619-2014   AbstractWebsite

Cyanobacteria, primarily of the species Nodularia spumigena, form extensive surface accumulations in the Baltic Sea in July and August, ranging from diffuse flakes to dense surface scums. The area of these accumulations can reach similar to 200 000 km(2). We describe the compilation of a 35-year-long time series (1979-2013) of cyanobacteria surface accumulations in the Baltic Sea using multiple satellite sensors. This appears to be one of the longest satellite-based time series in biological oceanography. The satellite algorithm is based on remote sensing reflectance of the water in the red band, a measure of turbidity. Validation of the satellite algorithm using horizontal transects from a ship of opportunity showed the strongest relationship with phycocyanin fluorescence (an indicator of cyanobacteria), followed by turbidity and then by chlorophyll a fluorescence. The areal fraction with cyanobacteria accumulations (FCA) and the total accumulated area affected (TA) were used to characterize the intensity and extent of the accumulations. The fraction with cyanobacteria accumulations was calculated as the ratio of the number of detected accumulations to the number of cloud-free sea-surface views per pixel during the season (July-August). The total accumulated area affected was calculated by adding the area of pixels where accumulations were detected at least once during the season. The fraction with cyanobacteria accumulations and TA were correlated (R-2 = 0.55) and both showed large interannual and decadal-scale variations. The average FCA was significantly higher for the second half of the time series (13.8 %, 1997-2013) than for the first half (8.6 %, 1979-1996). However, that does not seem to represent a long-term trend but decadal-scale oscillations. Cyanobacteria accumulations were common in the 1970s and early 1980s (FCA between 11-17 %), but rare (FCA below 4 %) during 1985-1990; they increased again starting in 1991 and particularly in 1999, reaching maxima in FCA (similar to 25 %) and TA (similar to 210 000 km(2)) in 2005 and 2008. After 2008, FCA declined to more moderate levels (6-17 %). The timing of the accumulations has become earlier in the season, at a mean rate of 0.6 days per year, resulting in approximately 20 days advancement during the study period. The interannual variations in FCA are positively correlated with the concentration of chlorophyll a during July-August sampled at the depth of similar to 5 m by a ship of opportunity, but interannual variations in FCA are more pronounced as the coefficient of variation is over 5 times higher.

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.

2012
Kahru, M, Di Lorenzo E, Manzano-Sarabia M, Mitchell BG.  2012.  Spatial and temporal statistics of sea surface temperature and chlorophyll fronts in the California Current. Journal of Plankton Research. 34:749-760.   10.1093/plankt/fbs010   AbstractWebsite

The statistics of sea-surface fronts detected with the automated histogram method were studied in the California Current using sea-surface temperature (SST) and chlorophyll-a concentration (Chl) images from various satellite sensors. Daily maps of fronts were averaged into monthly composites of front frequency (FF) spanning 29 years (19812009) for SST and 14 years (19972010) for Chl. The large-scale distributions of frontal frequency of both SST (FFsst) and of Chl (FFchl) had a 500700 km wide band of elevated values (47) along the coast that roughly coincided with the area of increased mesoscale eddy activity. FFsst and FFchl were positively correlated at monthly and seasonal frequencies, but the year-to-year variations were not significantly correlated. The long-period (1 year and longer) variability in FFsst is influenced by the large-scale SST gradient, while at shorter timescales the influence of the Coastal Upwelling Index is evident. In contrast with FFsst, FFchl variability is less related to the coherent large-scale forcing and has stronger sensitivity to local forcings in individual areas. Decadal-scale increasing trends in the frequency of both SST and Chl fronts were detected in the Ensenada Front area (general area of the A-Front study) and corresponded to, respectively, trends towards colder SST and increasing chlorophyll-a concentration.

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.

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.

2009
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.

2008
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.

2006
Murakami, H, Sasaoka K, Hosoda K, Fukushima H, Toratani M, Frouin R, Mitchell BG, Kahru M, Deschamps PY, Clark D, Flora S, Kishino M, Saitoh S, Asanuma I, Tanaka A, Sasaki H, Yokouchi K, Kiyomoto Y, Saito H, Dupouy C, Siripong A, Matsumura S, Ishizaka J.  2006.  Validation of ADEOS-II GLI ocean color products using in-situ observations. Journal of Oceanography. 62:373-393.   10.1007/s10872-006-0062-6   AbstractWebsite

The Global Imager (GLI) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) made global observations from 2 April 2003 to 24 October 2003. In cooperation with several institutes and scientists, we obtained quality controlled match-ups between GLI products and in-situ data, 116 for chlorophyll-a concentration (CHLA), 249 for normalized water-leaving radiance (nLw) at 443 nm, and 201 for aerosol optical thickness at 865 nm (Tau_865) and Angstrom exponent between 520 and 865 nm (Angstrom). We evaluated the GLI ocean color products and investigated the causes of errors using the match-ups. The median absolute percentage differences (MedPD) between GLI and in-situ data were 14.1-35.7% for nLws at 380-565 nm 52.5-74.8% nLws at 625-680 nm, 47.6% for Tau_865, 46.2% for Angstrom, and 46.6% for CHLA, values that are comparable to the ocean-color products of other sensors. We found that some errors in GLI products are correlated with observational conditions; nLw values were underestimated when nLw at 680 nm was high, CHLA was underestimated in absorptive aerosol conditions, and Tau_865 was overestimated in sunglint regions. The error correlations indicate that we need to improve the retrievals of the optical properties of absorptive aerosols and seawater and sea surface reflection for further applications, including coastal monitoring and the combined use of products from multiple sensors.

Smith, KL, Baldwin RJ, Ruhl HA, Kahru M, Mitchell BG, Kaufmann RS.  2006.  Climate effect on food supply to depths greater than 4,000 meters in the northeast Pacific. Limnology and Oceanography. 51:166-176. AbstractWebsite

A long time-series Study was conducted over 15 yr (1989-2004) to measure particulate organic carbon (POC) flux as an estimate of food supply reaching > 4,000-m depth in the northeast Pacific. Sequencing sediment traps were moored at 3,500-and 4,050-m depth, 600 and 50 in above the seafloor, respectively, to collect sinking particulate matter with 10-d resolution. POC fluxes were compared with three climate indices in the Pacific: the basin-scale multivariate El Nino Southern Oscillation index (MEI) and northern Oscillation index (NOI) and the regional-scale Bakun upwelling index (BUI). The NOI and MEI correlated significantly with POC flux, lagged earlier by 6-10 months, respectively. The BUI also correlated with POC flux. lagged by 2-3 months, suggesting a direct relationship between upwelling intensity and rates Of POC Supply to abyssal depths. Satellite ocean color data for the surface above the study site were used to estimate chlorophyll a concentrations and, combined with sea surface temperature and photosynthetically available radiation, to estimate net primary production and export flux (EF) from the euphotic zone. EF was significantly correlated with POC flux. lagged earlier by 0-3 months. An empirical model to estimate POC flux, with the use of NOI, BUI, and EF yielded Significant agreement with measured fluxes. Modeling of deep-sea processes on broad spatial and temporal scales with climate indices and satellite sensing now appears feasible.

2004
Kahru, M, Marinone SG, Lluch-Cota SE, Pares-Sierra A, Mitchell BG.  2004.  Ocean-color variability in the Gulf of California: scales from days to ENSO. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 51:139-146.   10.1016/j.dsr2.2003.04.001   AbstractWebsite

Time series of surface chlorophyll a concentration (C-sat) and phytoplankton net primary production (NPP) in the Gulf of California were derived using satellite data from OCTS, SeaWiFS, MODIS, AVHRR and the VGPM primary productivity model. The 6-year (1997-2003) time series showed variability at a multitude of scales. The annual cycle was the dominant mode in Gat variability in the entire gulf, except just south of the midriff islands where the semiannual cycle dominated. The semiannual cycle has C-sat maxima during the spring and fall transition periods when the general circulation is switching between cyclonic in the summer and anticyclonic in the winter and is less developed, therefore allowing a more efficient tidal mixing. The spring and fall maxima often consisted of multiple peaks of about 10 days. A significant peak at about 1 month was often present in the short-term C-sat variability, especially in areas near the midriff islands, suggesting the influence of tidal mixing. The interannual variability was dominated by the 1997-98 El Nino and the following La Nina. During the El Nino period NPP decreased by 30-40% in the southern part of the gulf (by approximately 1 Tg C month(-1)), but the changes in the central and northern parts were less evident. (C) 2004 Elsevier Ltd. All rights reserved.

2002
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.

1998
Mitchell, BG, Kahru M.  1998.  Algorithms for SeaWiFS standard products developed with the CalCOFI big-optical data set. California Cooperative Oceanic Fisheries Investigations Reports. 39:133-147. AbstractWebsite

Funding from NASA's Ocean Biogeochemistry Program and the Goddard Space Flight Center SeaWiFS Project was used to implement an ocean optics program as part of the routine cruises of the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Since August 1993, data from more than 300 bio-optical stations have been acquired, merged with complementary data, and made available for developing remote sensing algorithms. The profiling instrument consisted of a Biospherical Instruments, Inc. MER-2040/2041 radiometer integrated with CTD probes, a transmissometer, and a fluorometer. A detailed calibration time series of the radiance and irradiance sensors has been maintained to ensure maximum accuracy. The data set has been used to develop empirical algorithms for Sea WiFS standard products including chlorophyll a (chl a), "CZCS pigments," and diffuse attenuation coefficient K-d(490). Algorithms using cubic regressions of remote sensing reflectance (R-rs) ratios provided the best estimation of chi a and pigments over the full range of chl a (0.05-22.3 mg m(-3)). Multiple linear regressions of multiple-band ratios proved to be less robust. Relationships between spectral K and chi a suggest that previous K algorithms may have errors due to estimates of pure-water absorption.