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2017
Stukel, MR, Aluwihare LI, Barbeau KA, Chekalyuk AM, Goericke R, Miller AJ, Ohman MD, Ruacho A, Song H, Stephens BM, Landry MR.  2017.  Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction. Proceedings of the National Academy of Sciences of the United States of America. 114:1252-1257.   10.1073/pnas.1609435114   AbstractWebsite

Enhanced vertical carbon transport (gravitational sinking and subduction) at mesoscale ocean fronts may explain the demonstrated imbalance of new production and sinking particle export in coastal upwelling ecosystems. Based on flux assessments from U-238:Th-234 disequilibrium and sediment traps, we found 2 to 3 times higher rates of gravitational particle export near a deep-water front (305 mg C.m(-2).d(-1)) compared with adjacent water or to mean (nonfrontal) regional conditions. Elevated particle flux at the front wasmechanistically linked to Fe-stressed diatoms and high-mesozooplankton fecal pellet production. Using a data assimilative regional ocean model fit to measured conditions, we estimate that an additional similar to 225 mg C.m(-2).d(-1) was exported as subduction of particle-rich water at the front, highlighting a transport mechanism that is not captured by sediment traps and is poorly quantified by most models and in situ measurements. Mesoscale fronts may be responsible for over a quarter of total organic carbon sequestration in the California Current and other coastal upwelling ecosystems.

2016
Lindegren, M, Checkley DM, Ohman MD, Koslow JA, Goericke R.  2016.  Resilience and stability of a pelagic marine ecosystem. Proceedings of the Royal Society B-Biological Sciences. 283   10.1098/rspb.2015.1931   AbstractWebsite

The accelerating loss of biodiversity and ecosystem services worldwide has accentuated a long-standing debate on the role of diversity in stabilizing ecological communities and has given rise to a field of research on biodiversity and ecosystem functioning (BEF). Although broad consensus has been reached regarding the positive BEF relationship, a number of important challenges remain unanswered. These primarily concern the underlying mechanisms by which diversity increases resilience and community stability, particularly the relative importance of statistical averaging and functional complementarity. Our understanding of these mechanisms relies heavily on theoretical and experimental studies, yet the degree to which theory adequately explains the dynamics and stability of natural ecosystems is largely unknown, especially in marine ecosystems. Using modelling and a unique 60-year dataset covering multiple trophic levels, we show that the pronounced multi-decadal variability of the Southern California Current System (SCCS) does not represent fundamental changes in ecosystem functioning, but a linear response to key environmental drivers channelled through bottom-up and physical control. Furthermore, we show strong temporal asynchrony between key species or functional groups within multiple trophic levels caused by opposite responses to these drivers. We argue that functional complementarity is the primary mechanism reducing community variability and promoting resilience and stability in the SCCS.

2015
Stukel, MR, Kahru M, Benitez-Nelson CR, Decima M, Goericke R, Landry MR, Ohman MD.  2015.  Using Lagrangian-based process studies to test satellite algorithms of vertical carbon flux in the eastern North Pacific Ocean. Journal of Geophysical Research-Oceans. 120:7208-7222.   10.1002/2015jc011264   AbstractWebsite

The biological carbon pump is responsible for the transport of similar to 5-20 Pg C yr(-1) from the surface into the deep ocean but its variability is poorly understood due to an incomplete mechanistic understanding of the complex underlying planktonic processes. In fact, algorithms designed to estimate carbon export from satellite products incorporate fundamentally different assumptions about the relationships between plankton biomass, productivity, and export efficiency. To test the alternate formulations of export efficiency in remote-sensing algorithms formulated by Dunne et al. (2005), Laws et al. (2011), Henson et al. (2011), and Siegel et al. (2014), we have compiled in situ measurements (temperature, chlorophyll, primary production, phytoplankton biomass and size structure, grazing rates, net chlorophyll change, and carbon export) made during Lagrangian process studies on seven cruises in the California Current Ecosystem and Costa Rica Dome. A food-web based approach formulated by Siegel et al. (2014) performs as well or better than other empirical formulations, while simultaneously providing reasonable estimates of protozoan and mesozooplankton grazing rates. By tuning the Siegel et al. (2014) algorithm to match in situ grazing rates more accurately, we also obtain better in situ carbon export measurements. Adequate representations of food-web relationships and grazing dynamics are therefore crucial to improving the accuracy of export predictions made from satellite-derived products. Nevertheless, considerable unexplained variance in export remains and must be explored before we can reliably use remote sensing products to assess the impact of climate change on biologically mediated carbon sequestration.

Brzezinski, MA, Krause JW, Bundy RM, Barbeau KA, Franks P, Goericke R, Landry MR, Stukel MR.  2015.  Enhanced silica ballasting from iron stress sustains carbon export in a frontal zone within the California Current. Journal of Geophysical Research-Oceans. 120:4654-4669.   10.1002/2015jc010829   AbstractWebsite

Nutrient dynamics, phytoplankton rate processes, and export were examined in a frontal region between an anticyclone and a pair of cyclones 120 km off the coast in the southern California Current System (sCCS). Low silicic acid: nitrate ratios (Si:N) and high nitrate to iron ratios (N: Fe) characteristic of Fe-limiting conditions in the sCCS were associated with the northern cyclone and with the transition zone between the cyclones and the anticyclone. Phytoplankton growth in low-Si:N, high-N:Fe waters responded strongly to added Fe, confirming growth limitation by Fe of the diatom-dominated phytoplankton community. Low Si: N waters had low biogenic silica content, intermediate productivity, but high export compared to intermediate Si: N waters indicating increased export efficiency under Fe stress. Biogenic silica and particulate organic carbon (POC) export were both high beneath low Si: N waters with biogenic silica export being especially enhanced. This suggests that relatively high POC export from low Si: N waters was supported by silica ballasting from Fe-limited diatoms. Higher POC export efficiency in low Si: N waters may have been further enhanced by lower rates of organic carbon remineralization due to reduced grazing of more heavily armored diatoms growing under Fe stress. The results imply that Fe stress can enhance carbon export, despite lowering productivity, by driving higher export efficiency.

Bograd, SJ, Buil MP, Di Lorenzo E, Castro CG, Schroeder ID, Goericke R, Anderson CR, Benitez-Nelson C, Whitney FA.  2015.  Changes in source waters to the Southern California Bight. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 112:42-52.   10.1016/j.dsr2.2014.04.009   AbstractWebsite

Historical hydrographic data (1984-2012) from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) program and global reanalysis products were used to quantify recent water mass variability off the coast of Southern California. Dissolved oxygen concentrations continued to decline within the lower pycnocline, concurrent with strong increases in nitrate and phosphate that have spatial patterns matching those of dissolved oxygen. Silicic acid also shows an increasing trend in the offshore portion of the region, but has strong and opposing trends in the upper (increasing) and lower-pycnocline (decreasing) within the Southern California Bight. The varying rates of change in the inorganic nutrients yield a more complex pattern of variability in the nutrient ratios, resulting in large decreases in the N:P and Si:N ratios within the Southern California Bight at depths that provide source waters for upwelling. Basin-scale reanalysis products are consistent with low-frequency water mass changes observed off Southern California and suggest that advection of modified source waters is the cause of the variability. The biogeochemical changes described here may have important impacts on the regional ecosystem, including a reduction of viable pelagic habitat and community reorganization. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Sydeman, WJ, Thompson SA, Santora JA, Koslow JA, Goericke R, Ohman MD.  2015.  Climate-ecosystem change off southern California: Time-dependent seabird predator-prey numerical responses. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 112:158-170.   10.1016/j.dsr2.2014.03.008   AbstractWebsite

Climate change may increase both stratification and upwelling in marine ecosystems, but these processes may affect productivity in opposing or complementary ways. For the Southern California region of the California Current Ecosystem (CCE), we hypothesized that changes in stratification and upwelling have affected marine bird populations indirectly through changes in prey availability. To test this hypothesis, we derived trends and associations between stratification and upwelling, the relative abundance of potential prey including krill and forage fish, and seabirds based on the long-term, multi-disciplinary CalCOFI/CCE-LTER program. Over the period 1987 through 2011, spring and summer seabird density (all species combined) declined by similar to 2% per year, mostly in the northern sector of the study region. Krill showed variable trends with two species increasing and one deceasing, resulting in community reorganization. Nearshore forage fish, dominated by northern anchovy (Engraulis mordax) as well as offshore mesopelagic species, show declines in relative abundance over this period. The unidirectional decline in springtime seabird density is largely explained by declining nearshore fish abundance in the previous season (winter). Interannual variability in seabird density, especially in the 2000s, is explained by variability in krill abundance. Changes in the numerical responses of seabirds to prey abundance correspond to a putative ecosystem shift in 1998-1999 and support aspects of optimal foraging (diet) theory. Predator-prey interactions and numerical responses clearly explain aspects of the upper trophic level patterns of change in the pelagic ecosystem off southern California. (C) 2014 Elsevier Ltd. All rights reserved.

Goericke, R, Bograd SJ, Grundle DS.  2015.  Denitrification and flushing of the Santa Barbara Basin bottom waters. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 112:53-60.   10.1016/j.dsr2.2014.07.012   AbstractWebsite

The sediments of the Santa Barbara Basin (SBB) are an important paleoecological resource since their structure reflects the oxygenation of the bottom waters and the quality and quantity of the particulate matter which is sequestered to the bottom of the basin. These properties are controlled by regional atmospheric and oceanic climate. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) program has been monitoring the bottom waters of the SBB on a regular basis since 1986. Over the last decade, properties of SBB bottom waters have undergone dramatic changes: low concentrations of nitrate were observed more frequently and concentrations of nitrite, at times, reached values of 7 mu M, in contrast to maximum concentrations of 0.2 mu M observed during the earlier time period. Here we study the links between regional climate and conditions at the bottom of the SBB by relating recent changes in bottom water chemistry to local and regional forcing of the basin. Varying rates of primary production of the overlying water or rates of export production were not significantly related to the observed biogeochemical changes in the basin. Rather, the frequency or rate of flushing, as inferred from phosphate concentration changes at the bottom of the basin, and decreasing concentrations of oxygen in the waters outside the basins could be related to the observed changes. The episodic more than 10-fold increases of nitrite in the bottom waters likely represent a tipping point in the biogeochemical system driven by decreasing concentrations of oxygen in the bottom waters. (C) 2014 Elsevier Ltd. All rights reserved.

Leising, AW, Schroeder ID, Bograd SJ, Abell J, Durazo R, Gaxiola-Castro G, Bjorkstedt EP, Field J, Sakuma K, Robertson RR, Goericke R, Peterson WT, Brodeur R, Barcelo C, Auth TD, Daly EA, Suryan RM, Gladics AJ, Porquez JM, McClatchie S, Weber ED, Watson W, Santora JA, Sydeman WJ, Melin SR, Chavez FP, Golightly RT, Schneider SR, Fisher J, Morgan C, Bradley R, Warybok P.  2015.  State of the California Current 2014-15: Impacts of the warm-water "blob". California Cooperative Oceanic Fisheries Investigations Reports. 56:31-68. AbstractWebsite

In 2014, the California Current (similar to 28 degrees-48 degrees N) saw average, or below average, coastal upwelling and relatively low productivity in most locations, except from 38 degrees-43 degrees N during June and July. Chlorophyll-a levels were low throughout spring and summer at most locations, except in a small region around 39 degrees N. Catches of juvenile rockfish (an indicator of upwelling-related fish species) remained high throughout the area surveyed (32 degrees-43 degrees N). In the fall of 2014, as upwelling ceased, many locations saw an unprecedented increase in sea surface temperatures (anomalies as large as 4 degrees C), particularly at 45 degrees N due to the coastal intrusion of an extremely anomalous pool of warm water. This warm surface anomaly had been building offshore in the Gulf of Alaska since the fall of 2013, and has been referred to as the "blob." Values of the Pacific Decadal Oscillation index (PDO) continued to climb during 2014, indicative of the increase in warm coastal surface waters, whereas the North Pacific Gyre Oscillation index (NPGO) saw a slight rebound to more neutral values (indicative of average productivity levels) during 2014. During spring 2015, the upwelling index was slightly higher than average for locations in the central and northern region, but remained below average at latitudes south of 35 degrees N. Chlorophyll a levels were slightly higher than average in similar to 0.5 degrees latitude patches north of 35 degrees N, whereas productivity and phytoplankton biomass were low south of Pt. Conception. Catches of rockfish remained high along most of the coast, however, market squid remained high only within the central coast (36 degrees-38 degrees N), and euphausiid abundance decreased everywhere, as compared to the previous year. Sardine and anchovy were nearly absent from the southern portion of the California Current system (CCS), whereas their larvae were found off the coast of Oregon and Washington during winter for the first time in many years. Waters warmed dramatically in the southern California region due to a change in wind patterns similar to that giving rise to the blob in the broader northeast Pacific. For most of the coast, there were intrusions of species never found before or found at much higher abundances than usual, including fish, crustaceans, tunicates and other gelatinous zooplankton, along with other species often indicative of an El Nino. Thus species richness was high in many areas given the close juxtaposition of coastal upwelling-related species with the offshore warm-water intrusive or El Nino-typical taxa. Thus the California Current by 2015 appears to have transitioned to a very different state than previous observations.

2014
McClatchie, S, Duffy-Anderson J, Field JC, Goericke R, Griffith D, Hanisko DS, Hare JA, Lyczkowski-Shultz J, Peterson WT, Watson W, Weber ED, Zapfe G.  2014.  Long time series in U.S. fisheries oceanography. Oceanography. 27:48-67.   10.5670/oceanog.2014.86   AbstractWebsite

Few fisheries oceanography surveys in the United States have sampled hydrography and ichthyoplankton or juvenile fishes for 15 years or more. We describe six long time series surveys, including three from the California Current System, and one each from Alaska (Gulf of Alaska, Bering Sea, and the Arctic), the Northeast US Shelf, and the Gulf of Mexico. We examine the applications of long time series data as well as the output of published analyses, Web-based graphical summaries, and quality controlled data to the broader scientific community (including resource managers and stakeholders). Potential improvements to the surveys using new technologies are evaluated, and possible changes in survey design are discussed. We conclude with a summary of the benefits derived from these long time series fisheries oceanography surveys and make the case for their continuation.

Wang, SY, Lambert W, Giang S, Goericke R, Palenik B.  2014.  Microalgal assemblages in a poikilohaline pond. Journal of Phycology. 50:303-309.   10.1111/jpy.12158   AbstractWebsite

Microalgal strains for algal biofuels production in outdoor ponds will need to have high net growth rates under diverse environmental conditions. A small, variable salinity pond in the San Elijo Lagoon estuary in southern California was chosen to serve as a model pond due to its routinely high chlorophyll content. Profiles of microalgal assemblages from water samples collected from April 2011 to January 2012 were obtained by constructing 18S rDNA environmental clone libraries. Pond assemblages were found to be dominated by green algae Picochlorum sp. and Picocystis sp. throughout the year. Pigment analysis suggested that the two species contributed most of the chlorophyll a of the pond, which ranged from 21.9 to 664.3 mu g center dot L-1 with the Picocystis contribution increasing at higher salinities. However, changes of temperature, salinity or irradiance may have enabled a bloom of the diatom Chaetoceros sp. in June 2011. Isolates of these microalgae were obtained and their growth rates characterized as a function of temperature and salinity. Chaetoceros sp. had the highest growth rate over the temperature test range while it showed the most sensitivity to high salinity. All three strains showed the presence of lipid bodies during nitrogen starvation, suggesting they have potential as future biofuels strains.

2013
Ohman, MD, Barbeau K, Franks PJS, Goericke R, Landry MR, Miller AJ.  2013.  Ecological transitions in a coastal upwelling ecosystem. Oceanography. 26:210-219. AbstractWebsite

The southern California Current Ecosystem (CCE) is a dynamic eastern boundary current ecosystem that is forced by ocean-atmosphere variability on interannual, multidecadal, and long-term secular time scales. Recent evidence suggests that apparent abrupt transitions in ecosystem conditions reflect linear tracking of the physical environment rather than oscillations between alternative preferred states. A space-for-time exchange is one approach that permits use of natural spatial variability in the CCE to develop a mechanistic understanding needed to project future temporal changes. The role of (sub)mesoscale frontal systems in altering rates of nutrient transport, primary and secondary production, export fluxes, and the rates of encounters between predators and prey is an issue central to this pelagic ecosystem and its future trajectory because the occurrence of such frontal features is increasing.

Munro, DR, Quay PD, Juranek LW, Goericke R.  2013.  Biological production rates off the Southern California coast estimated from triple O-2 isotopes and O-2 : Ar gas ratios. Limnology and Oceanography. 58:1312-1328.   10.4319/lo.2013.58.4.1312   AbstractWebsite

The isotopic composition of dissolved O-2 ((17)Delta) and the biological O-2 saturation from O-2 : Ar ratios were measured in the surface ocean during six cruises off the coast of southern California from November 2005 to August 2008 to determine rates of gross oxygen production (GOP), net oxygen production (NOP), and the NOP:GOP ratio (a measure of potential export efficiency). In the mixed layer, (17)Delta of dissolved O-2 (17 Delta(diss)) ranged from 24 to 108 per meg and biological O-2 saturation ranged from 101% to 113% for all regions and cruises. Mixed-layer (17)Delta-GOP ranged from 49 +/- 23 mmol O-2 m(-2) d(-1) to 533 +/- 185 mmol O-2 m(-2) d(-1) with an annual mean for the California Cooperative Oceanic Fisheries Investigations (CalCOFI) grid of 151 +/- 59 mmol O-2 m(-2) d(-1). Mixed-layer O-2 : Ar-NOP ranged from 8 +/- 6 mmol O-2 m(-2) d(-1) to 135 +/- 31 mmol O-2 m(-2)d(-1) with an annual mean of 25 +/- 8 mmol O-2 m(-2) d(-1), implying that the CalCOFI grid is autotrophic year-round. (17)Delta-GOP estimates were consistently greater than on-deck incubation-based C-14-primary production (C-14-PP) by a factor of 5.6 +/- 6 0.4 and greater than satellite PP estimates by a factor of 3.5 +/- 0.3 (mmol O-2 : mmol C). The (17)Delta-GOP to C-14-PP factor was twice the expected factor of 2.7 determined from comparisons of incubation-based O-18-GOP and C-14-PP. The annual mean NOP: GOP ratio was 0.16 +/- 0.06, suggesting a potential export efficiency that is surprisingly similar to the open ocean using comparable methods.

Wells, BK, Schroeder ID, Santora JA, Hazen EL, Bograd SJ, Bjorkstedt EP, Loeb VJ, McClatchie S, Weber ED, Watson W, Thompson AR, Peterson WT, Brodeur RD, Harding J, Field J, Sakuma K, Hayes S, Mantua N, Sydeman WJ, Losekoot M, Thompson SA, Largier J, Kim SY, Chavez FP, Barcelo C, Warzybok P, Bradley R, Jahncke J, Goericke R, Campbell GS, Hildebrand JA, Melin SR, DeLong RL, Gomez-Valdes J, Lavaniegos B, Gaxiola-Castro G, Golightly RT, Schneider SR, Lo N, Suryan RM, Gladics AJ, Horton CA, Fisher J, Morgan C, Peterson J, Daly EA, Auth TD, Abell J.  2013.  State of the California current 2012-13: No such thing as an "average" year. California Cooperative Oceanic Fisheries Investigations Reports. 54:37-71. AbstractWebsite

This report reviews the state of the California Current System (CCS) between winter 2012 and spring 2013, and includes observations from Washington State to Baja California. During 2012, large-scale climate modes indicated the CCS remained in a cool, productive phase present since 2007. The upwelling season was delayed north of 42 degrees N, but regions to the south, especially 33 degrees to 36 degrees N, experienced average to above average upwelling that persisted throughout the summer. Contrary to the indication of high production suggested by the climate indices, chlorophyll observed from surveys and remote sensing was below average along much of the coast. As well, some members of the forage assemblages along the coast experienced low abundances in 2012 surveys. Specifically, the concentrations of all life-stages observed directly or from egg densities of Pacific sardine, Sardinops sagax, and northern anchovy, Engraulis mordax, were less than previous years' survey estimates. However, 2013 surveys and observations indicate an increase in abundance of northern anchovy. During winter 2011/2012, the increased presence of northern copepod species off northern California was consistent with stronger southward transport. Krill and small-fraction zooplankton abundances, where examined, were generally above average. North of 42 degrees N, salps returned to typical abundances in 2012 after greater observed concentrations in 2010 and 2011. In contrast, salp abundance off central and southern California increased after a period of southward transport during winter 2011/2012. Reproductive success of piscivorous Brandt's cormorant, Phalacrocorax penicillatus, was reduced while planktivorous Cassin's auklet, Ptychoramphus aleuticus was elevated. Differences between the productivity of these two seabirds may be related to the available forage assemblage observed in the surveys. California sea lion pups from San Miguel Island were undernourished resulting in a pup mortality event perhaps in response to changes in forage availability. Limited biological data were available for spring 2013, but strong winter upwelling coastwide indicated an early spring transition, with the strong upwelling persisting into early summer.

Anthony Koslow, J, Goericke R, Watson W.  2013.  Fish assemblages in the Southern California Current: relationships with climate, 1951–2008. Fisheries Oceanography. 22:207-219.   10.1111/fog.12018   AbstractWebsite

We examined the dominant patterns of variability in the fish fauna of the southern California Current based on a principal component (PC) analysis of the California Cooperative Oceanic Fisheries Investigations ichthyoplankton data set, 1951–2008. Eighty-six taxa were analyzed, including all ecologically dominant fish species, both exploited and unexploited. The first three PCs accounted for 20.5, 12.4 and 6.8% of the variance of the data, respectively (total: 39.7%). Each was dominated by taxa from particular adult or larval habitats. PC 1 predominantly represented the coherent response of 24 mesopelagic taxa from 10 families and was most highly correlated with long-term trends in midwater oxygen levels. PC 2 was dominated by six of the seven most abundant ichthyoplankton taxa in the region, predominantly California Current endemics including key pelagic species (northern anchovy, Pacific sardine and Pacific hake), rockfishes (genus Sebastes) and two midwater taxa. It was correlated primarily with sea surface temperature and exhibited a significant declining trend. PC 3 was dominated by coastal and reef-associated fishes with predominantly southerly affinities. It was positively correlated with sea surface temperature and sea level height, a proxy for diminished flow of the California Current. The taxa dominating PCs 2 and 3 mostly spatially co-occur as ichthyoplankton. These results suggest that fish assemblages in the California Current are predominantly influenced by environmental forcing of their ocean habitats as adults or larvae, or both.

2012
Chekalyuk, AM, Landry MR, Goericke R, Taylor AG, Hafez MA.  2012.  Laser fluorescence analysis of phytoplankton across a frontal zone in the California Current ecosystem. Journal of Plankton Research. 34:761-777.   10.1093/plankt/fbs034   AbstractWebsite

Spatial variability of chlorophyll, phycobiliproteins, chromophoric dissolved organic matter and variable fluorescence (F-v/F-m) was analyzed across a deep-water density front in the Southern California Current Ecosystem using an Advanced Laser Fluorometer (ALF) calibrated to assess chlorophyll concentration (C-chl), total autotrophic carbon (AC) and Synechococcus carbon biomass (SYN). Three distinct autotrophic assemblages were identified. Fluorescence was found to be three to four times higher in cooler mesotrophic waters north of the front than in warm oligotrophic waters to the south. Northern waters were distinguished by a shallow pigment maximum dominated by a blue-water type of Synechococcus and by the presence of green-water Synechococcus and cryptophytes; only blue-water Synechococcus were detected at lower concentration south of the front. The highest C-chl and AC values, accompanied by elevated F-v/F-m and chlorophyll fluorescence per unit of C-chl, and minimal Synechococcus abundance, were found directly at the front in a 2040 m deep layer dominated by diatoms. The covariation of F-v/F-m with nitrate concentration in this layer, along with the structural changes in the phytoplankton community, suggest that it had been generated by in situ processes rather than advection. Strong structural responses to the local hydrography were also revealed by high-frequency underway ALF surface sampling, which detected an abrupt transition from low to high SYN on the northern side of a sharp salinity gradient at the front. Synechococcus-specific phycoerythrin fluorescence (F-PE12) and SYN were highly correlated in surface waters (R-2 0.95), while F-PE12:SYN gradually increased with depth. Strong relationships were found for chlorophyll fluorescence versus C-chl (R-2 0.95) and AC (R-2 0.79).

Samo, TJ, Pedler BE, Ball GI, Pasulka AL, Taylor AG, Aluwihare LI, Azam F, Goericke R, Landry MR.  2012.  Microbial distribution and activity across a water mass frontal zone in the California Current Ecosystem. Journal of Plankton Research. 34:802-814.   10.1093/plankt/fbs048   AbstractWebsite

Ocean fronts with accumulated biomass and organic matter may be significant sites of enhanced microbial activity. We sampled a frontal region (the A-Front) separating oligotrophic and mesotrophic water masses within the California Current Ecosystem (CCE) to assess the influence of frontal hydrography on several microbial parameters. Samples for heterotrophic bacterial, viral and flagellate abundance, dissolved and particulate carbon and nitrogen, transparent particles and bacterial carbon production were collected at 6 depths from the surface to 100 m with 59 conductivity/temperature/depth casts along a 26-km northerly transect across the front. Relative to adjacent oligotrophic and mesotrophic waters, the frontal transition displayed peaks in the mean estimates of cell-specific bacterial carbon and bulk bacterial production, particulate organic carbon and particulate organic nitrogen concentrations, and the abundance and size of transparent particles. Bacterial carbon production increased approximate to 5-fold northward from oligotrophic waters to the frontal zone, in agreement with an increase in the frequency of dividing cells, but bacterial abundance was lower than at adjacent stations. This may be partially explained by high chlorophyll, elevated virus:bacteria ratios and low nanoflagellate grazer abundance at the front. Our data suggest that CCE fronts can facilitate intense biological transformation and physical transport of organic matter, in sharp contrast to adjacent low productivity waters, and harbor dynamic microbial populations that influence nutrient cycling.

Landry, MR, Ohman MD, Goericke R, Stukel MR, Barbeau KA, Bundy R, Kahru M.  2012.  Pelagic community responses to a deep-water front in the California Current Ecosystem: overview of the A-Front Study. Journal of Plankton Research. 34:739-748.   10.1093/plankt/fbs025   AbstractWebsite

In October 2008, we investigated pelagic community composition and biomass, from bacteria to fish, across a sharp frontal gradient overlying deep waters south of Point Conception, California. This northsouth gradient, which we called A-Front, was formed by the eastward flow of the California Current and separated cooler mesotrophic waters of coastal upwelling origin to the north, from warm oligotrophic waters of likely mixed subarcticsubtropical origin to the south. Plankton biomass and phytoplankton growth rates were two to three times greater on the northern side, and primary production rates were elevated 5-fold to the north. Compared with either of the adjacent waters, the frontal interface was strongly enriched and uniquely defined by a subsurface bloom of large diatoms, elevated concentrations of suspension-feeding zooplankton, high bioacoustical estimates of pelagic fish and enhanced bacterial production and phytoplankton biomass and photosynthetic potential. Such habitats, though small in areal extent, may contribute disproportionately and importantly to regional productivity, nutrient cycling, carbon fluxes and trophic ecology. As a general introduction to the A-Front study, we provide an overview of its design and implementation, a brief summary of major findings and a discussion of potential mechanisms of plankton enrichment at the front.

Taylor, AG, Goericke R, Landry MR, Selph KE, Wick DA, Roadman MJ.  2012.  Sharp gradients in phytoplankton community structure across a frontal zone in the California Current Ecosystem. Journal of Plankton Research. 34:778-789.   10.1093/plankt/fbs036   AbstractWebsite

Spatial variability of plankton biomass, community composition and size structure was investigated across a strong frontal transition (A-Front) in the southern California Current Ecosystem in October 2008. Depth profiles were taken across a 25-km transect of nine stations sampled semi-synoptically during one night and for 3 days following drifter arrays in the adjacent water masses. Community compositions are compared based on analyses by digital epifluorescence microscopy, flow cytometry and pigment composition by high-pressure liquid chromatography. Our results show three assemblages sharply delineated in space, with plankton at the front being compositionally distinct and biomass elevated relative to either of the adjacent water masses. Depth-averaged chlorophyll a (Chl a) varied by a factor of 2.3 (0.350.81 g Chl a L-1) and autotrophic carbon (AC) varied almost 3-fold (13.635.4 g C L-1) across the front. One of the most striking features was a sharp gradient in the distribution of Prochlorococcus (PRO) and Synechococcus (SYN), with PRO located in the warmer oligotrophic waters on the south side of the front and SYN located in the cooler mesotrophic waters to the north. Both PRO and SYN had local biomass minima directly at the front. The peak in phytoplankton biomass at the front was dominated by large (20 m) diatom cells, comprising 71 of the total community biomass. In contrast to previous studies of frontal features in the southern California Current, our study of the A-Front shows strong frontal enhancement of phytoplankton biomass and a shift of phytoplankton size structure towards larger cells.

Alin, SR, Feely RA, Dickson AG, Hernandez-Ayon JM, Juranek LW, Ohman MD, Goericke R.  2012.  Robust empirical relationships for estimating the carbonate system in the southern California Current System and application to CalCOFI hydrographic cruise data (2005-2011). Journal of Geophysical Research-Oceans. 117   10.1029/2011jc007511   AbstractWebsite

The California Current System (CCS) is expected to experience the ecological impacts of ocean acidification (OA) earlier than most other ocean regions because coastal upwelling brings old, CO2-rich water relatively close to the surface ocean. Historical inorganic carbon measurements are scarce, so the progression of OA in the CCS is unknown. We used a multiple linear regression approach to generate empirical models using oxygen (O-2), temperature (T), salinity (S), and sigma theta (sigma(theta)) as proxy variables to reconstruct pH, carbonate saturation states, carbonate ion concentration ([CO32-]), dissolved inorganic carbon (DIC) concentration, and total alkalinity (TA) in the southern CCS. The calibration data included high-quality measurements of carbon, oxygen, and other hydrographic variables, collected during a cruise from British Columbia to Baja California in May-June 2007. All resulting empirical relationships were robust, with r(2) values >0.92 and low root mean square errors. Estimated and measured carbon chemistry matched very well for independent data sets from the CalCOFI and IMECOCAL programs. Reconstructed CCS pH and saturation states for 2005-2011 reveal a pronounced seasonal cycle and inter-annual variability in the upper water column. Deeper in the water column, conditions are stable throughout the annual cycle, with perennially low pH and saturation states. Over sub-decadal time scales, these empirical models provide a valuable tool for reconstructing carbonate chemistry related to ocean acidification where direct observations are limited. However, progressive increases in anthropogenic CO2 content of southern CCS water masses must be carefully addressed to apply the models over longer time scales.

Stukel, MR, Landry MR, Ohman MD, Goericke R, Samo T, Benitez-Nelson CR.  2012.  Do inverse ecosystem models accurately reconstruct plankton trophic flows? Comparing two solution methods using field data from the California Current Journal of Marine Systems. 91:20-33.   10.1016/j.jmarsys.2011.09.004   AbstractWebsite

Despite the increasing use of linear inverse modeling techniques to elucidate fluxes in undersampled marine ecosystems, the accuracy with which they estimate food web flows has not been resolved. New Markov Chain Monte Carlo (MCMC) solution methods have also called into question the biases of the commonly used L(2) minimum norm (L(2)MN) solution technique. Here, we test the abilities of MCMC and L(2)MN methods to recover field-measured ecosystem rates that are sequentially excluded from the model input. For data, we use experimental measurements from process cruises of the California Current Ecosystem (CCE-LTER) Program that include rate estimates of phytoplankton and bacterial production, micro- and mesozooplankton grazing, and carbon export from eight study sites varying from rich coastal upwelling to offshore oligotrophic conditions. Both the MCMC and L(2)MN methods predicted well-constrained rates of protozoan and mesozooplankton grazing with reasonable accuracy, but the MCMC method overestimated primary production. The MCMC method more accurately predicted the poorly constrained rate of vertical carbon export than the L(2)MN method, which consistently overestimated export. Results involving DOC and bacterial production were equivocal. Overall, when primary production is provided as model input, the MCMC method gives a robust depiction of ecosystem processes. Uncertainty in inverse ecosystem models is large and arises primarily from solution under-determinacy. We thus suggest that experimental programs focusing on food web fluxes expand the range of experimental measurements to include the nature and fate of detrital pools, which play large roles in the model. (C) 2011 Elsevier B.V. All rights reserved.

Zhang, J, Fleming J, Goericke R.  2012.  Fishermen's perspectives on climate variability. Marine Policy. 36:466-472.   10.1016/j.marpol.2011.06.001   AbstractWebsite

Understanding fishermen's perspectives and responses relating to climate variability is important for sustainable fisheries management. To this end, a survey of captains of commercial passenger fishing vessels (CPFVs) was conducted in San Diego. The survey demonstrates that fishermen have observed and adapted to changes in the environment and fish populations associated with climate variability. However, only 12.9% of respondents agreed that global climate change is a possibility. In order to explain fishermen's divergent beliefs on climate change, a semiparametric discrete choice model is used to identify the potential determinants. The empirical results highlight the importance of the following factors: fishermen's experience, observations of the phenomena that are associated with climate variability, and an interaction of fishermen's experience and their observations. (C) 2011 Published by Elsevier Ltd.

Roth, MS, Goericke R, Deheyn DD.  2012.  Cold induces acute stress but heat is ultimately more deleterious for the reef-building coral Acropora yongei. Scientific Reports. 2   10.1038/srep00240   AbstractWebsite

Climate change driven increases in intensity and frequency of both hot and cold extreme events contribute to coral reef decline by causing widespread coral bleaching and mortality. Here, we show that hot and cold temperature changes cause distinct physiological responses on different time scales in reef-building corals. We exposed the branching coral Acropora yongei in individual aquaria to a +/- 5 degrees C temperature change. Compared to heat-treated corals, cold-treated corals initially show greater declines in growth and increases in photosynthetic pressure. However, after 2-3 weeks, cold-treated corals acclimate and show improvements in physiological state. In contrast, heat did not initially harm photochemical efficiency, but after a delay, photosynthetic pressure increased rapidly and corals experienced severe bleaching and cessation of growth. These results suggest that short-term cold temperature is more damaging for branching corals than short-term warm temperature, whereas long-term elevated temperature is more harmful than long-term depressed temperature.

Bjorkstedt, EP, Goericke R, McClatchie S, Weber E, Watson W, Lo N, Peterson WT, Brodeur RD, Auth T, Fisher J, Morgan C, Peterson J, Largier J, Bograd SJ, Durazo R, Gaxiola-Castro G, Lavaniegos B, Chavez FP, Collins CA, Hannah B, Field J, Sakuma K, Satterthwaite W, O'Farrell M, Hayes S, Harding J, Sydeman WJ, Thompson SA, Warzybok P, Bradley R, Jahncke J, Golightly RT, Schneider SR, Suryan RM, Gladics AJ, Horton CA, Kim SY, Melin SR, DeLong RL, Abell J.  2012.  STATE OF THE CALIFORNIA CURRENT 2011-2012: ECOSYSTEMS RESPOND TO LOCAL FORCING AS LA NINA WAVERS AND WANES. California Cooperative Oceanic Fisheries Investigations Reports. 53:41-76. AbstractWebsite

The state of the California Current System (CCS) since spring 2011 has evolved in response to dissipation of La Nina through spring and summer, resurgence of cooler La Nina conditions in fall and winter, and finally a transition towards ENSO-neutral conditions in spring 2012. The resurgence of La Nina was uneven, however, as indicated by variable responses in broad climate indices such as the Pacific Decadal Oscillation and the multi-variate ENSO index, and by latitudinal variability in the timing, strength, and duration of upwelling relative to climatological means. Across the CCS, various measures of ecosystem productivity exhibited a general decline in 2011 relative to 2010, but the magnitude of these declines varied substantially among taxa. Available observations indicate regional variability in climate forcing and ecosystem responses throughout the CCS, continuing a pattern that has emerged with increasing clarity over the past several years. In 2011-12, regional variability was again a consequence of southern regions exhibiting a relatively mild response to climate forcing, in this case tending towards climatological means, while northern regions showed somewhat greater effects of delayed or weaker-than-normal upwelling. In addition to the effects of local and basin-scale forcing, long-term observations off southern California show declines in dissolved oxygen and increases in nutrient concentrations in waters below the mixed layer, trends that are consistent with recent predictions of how global warming will affect the characteristics of upwelling source waters in the CCS. Such trends must be accounted for more comprehensively in ongoing assessment of the state of the California Current and its responses to environmental forcing. At the time of writing, tropical conditions are ENSO neutral and forecast to transition into El Nino in late 2012. This, combined with unusually high abundances of diverse gelatinous taxa throughout much of the CCS during spring 2012, suggests that the ongoing evolution of the state of the California Current might take a particularly unusual path in the coming year.

2011
Stukel, MR, Landry MR, Benitez-Nelson CR, Goericke R.  2011.  Trophic cycling and carbon export relationships in the California Current Ecosystem. Limnology and Oceanography. 56:1866-1878.   10.4319/lo.2011.56.5.1866   AbstractWebsite

We constructed a simple non-steady-state model of trophic cycling relationships in the California Current Ecosystem and tested its predictions of mesozooplankton fecal-pellet export against vertical carbon-flux measurements by the (234)Th method taken during Lagrangian experiments. To assess trophic relationships, we simultaneously measured (14)C-primary production and chlorophyll-based rate estimates of phytoplankton growth, microzooplankton grazing, mesozooplankton grazing, and net phytoplankton growth. Study locations ranged from coastal upwelling to offshore oligotrophic conditions. E-ratios (carbon export : (14)C-primary production) predicted by the model ranged from 0.08 to 0.14, in good agreement with both the magnitude and the variability found in contemporaneous measurements of (234)Th export and C: (234)Th-ratios of sinking particles. E-ratios were strongly decoupled from new production estimates. The lowest measured and predicted e-ratios were associated with higher nutrient chlorophyll parcels with net accumulating phytoplankton in the inshore region. For our study sites, variability in export efficiency was determined by the local net balance of growth and grazing and the relative strengths of grazing pathways to microzooplankton and mesozooplankton. Despite very different plankton assemblages studied, the consistently good agreement between independently measured production-grazing processes and biogeochemical rates suggest that zooplankton are the major drivers of vertical carbon-flux in this system during springtime.

Goericke, R.  2011.  THE SIZE STRUCTURE OF MARINE PHYTOPLANKTON-WHAT ARE THE RULES? California Cooperative Oceanic Fisheries Investigations Reports. 52:198-204. AbstractWebsite

It has been suggested that the size structure of marine phytoplankton communities varies with concentrations of chlorophyll a (CM a):When total biomass is low, biomass is added only to the smallest size class until an upper limit to Chl a in this size class-its biomass quota-has been reached. At this point biomass can only be added to the community by adding Chl a to the next larger size class until its quota too is reached, whereupon the next largest size class is filled up, etc. These rules predict a maximum biomass for all size classes, except for the largest one whose maximum biomass is set by the availability of inorganic nutrients, and abundance thresholds for all size classes except for the smallest one. Here these predictions were tested in a variety of environments, the California Current system, the Eastern Tropical North Pacific, and the Sargasso Sea. Even though the smallest and largest size classes followed the above rules, i.e., these had an upper biomass limit and an abundance threshold, respectively, biomass distributions