California Current Upwelling System Research Articles

Evaluation of Different Bias Correction Methods for Dynamical Downscaled Future Projections of the California Current Upwelling System

AbstractBiases in global Earth System Models (ESMs) are an important source of errors when used to obtain boundary conditions for regional models. Here we examine historical and future conditions in the California Current System (CCS) using three different methods to force the regional model: (a) interpolation of ESM output to the regional grid with no bias correction; (b) a “seasonally‐varying” delta method that obtains a season‐dependent mean climate change signal from the ESM for a 30‐year future period; and (c) a “time‐varying” delta method that includes the interannual variability of the ESM over the 1980–2100 period. To compare these methods, we use a high‐resolution (0.1°) physical‐biogeochemical regional model to dynamically downscale an ESM projection under the RCP8.5 emission scenario. Using different downscaling methods, the sign of future changes agrees for most of the physical and ecosystem variables, but the spatial patterns and magnitudes of these changes differ, with the seasonal‐ and time‐varying delta simulations showing more similar changes. Not correcting the ESM forcing leads to amplification of biases in some ecosystem variables as well as misrepresentation of the California Undercurrent and CCS source waters. In the non‐bias corrected and time‐varying delta simulations, most of the ecosystem variables inherit trends and decadal variability from the ESM, while in the seasonally‐varying delta simulation the future variability reflects the observed historical variability (1980–2010). Our results demonstrate that bias correcting the forcing prior to downscaling improves historical simulations, and that the bias correction method may impact the spatial and temporal variability of the future projections.

Coastal upwelling drives ecosystem temporal variability from the surface to the abyssal seafloor

Long-term biological time series that monitor ecosystems across the ocean's full water column are extremely rare. As a result, classic paradigms are yet to be tested. One such paradigm is that variations in coastal upwelling drive changes in marine ecosystems throughout the water column. We examine this hypothesis by using data from three multidecadal time series spanning surface (0 m), midwater (200 to 1,000 m), and benthic (~4,000 m) habitats in the central California Current Upwelling System. Data include microscopic counts of surface plankton, video quantification of midwater animals, and imaging of benthic seafloor invertebrates. Taxon-specific plankton biomass and midwater and benthic animal densities were separately analyzed with principal component analysis. Within each community, the first mode of variability corresponds to most taxa increasing and decreasing over time, capturing seasonal surface blooms and lower-frequency midwater and benthic variability. When compared to local wind-driven upwelling variability, each community correlates to changes in upwelling damped over distinct timescales. This suggests that periods of high upwelling favor increase in organism biomass or density from the surface ocean through the midwater down to the abyssal seafloor. These connections most likely occur directly via changes in primary production and vertical carbon flux, and to a lesser extent indirectly via other oceanic changes. The timescales over which species respond to upwelling are taxon-specific and are likely linked to the longevity of phytoplankton blooms (surface) and of animal life (midwater and benthos), which dictate how long upwelling-driven changes persist within each community.

Population projections of Pacific sardine driven by ocean warming and changing food availability in the California Current

Abstract Small pelagic fish are important marine ecosystem components and highly variable fisheries resources. In the California Current upwelling system, Pacific sardine (Sardinops sagax) has supported important fisheries in the past, but contrary to expectations, remains at low biomass despite recent warm ocean conditions. We developed a data-driven, process-based population model that reproduces fluctuations of the US Pacific sardine population based on ocean temperature, early life stage and adult food, and upwelling strength. The lack of sardine recovery after 2014 can be explained by reduced food availability. Ensemble projections for the 21st century driven by downscaled ocean-biogeochemical simulations under three Earth system models (ESMs) show a likely recovery to early 2000s sardine abundance and catch by mid-century, due to increased recruitment. Ecological process uncertainty (ensemble configuration range) is of the same magnitude as uncertainty among ESM projections, and uncertainty related to the thermal optimum of early life stages dominates after 2070. Even for a fish species presumably favoured by warmer conditions, future climate projections entail risks of stock declines in food-limited years and when passing unknown thermal optima. Quantification of combined environmental driver impacts and sources of uncertainty to projections under novel conditions open new pathways for environment-responsive fisheries management strategies.

El Niño and marine heatwaves: Ecological impacts on Oregon rocky intertidal kelp communities at local to regional scales

AbstractEl Niños and marine heatwaves (MHWs) are predicted to increase in frequency under greenhouse warming. The impact of climate oscillations like El Niño‐Southern Oscillation on coastal environments in the short term likely mimics those of climate change in the long term; therefore, El Niños may serve as a short‐term proxy for possible long‐term ecological responses to an increasingly variable climate. Understanding and prediction of ecosystem responses requires elucidating the mechanisms underlying different organizational scales (organism, space, and time). We analyzed spatiotemporal variation in the effect of the 2015–2016 El Niño and the overlapping 2014–2016 East Pacific MHW on three intertidal kelps (Hedophyllum sessile, Egregia menziesii, and Postelsia palmaeformis) at seven sites across 300 km of the Oregon coast and over three years post El Niño. We measured percent cover, density, maximum length, growth, and carbon : nitrogen (C:N) ratios monthly in spring/summer at each site from 2016 through 2018. Results revealed a complex interplay between spatial, temporal, and biological factors that modified the effects of these thermal anomalies on Oregon intertidal kelp populations. Our findings generally agree with prior literature showing detrimental effects of El Niño on kelp. However, El Niño and possibly MHW effects can be mitigated or amplified by environmental processes and kelp life history strategies. In our study, coastal upwelling provided regional relief for the kelp individuals with respect to their growth needs and mitigated the adverse effects of warming. On the other hand, we also found that coastal upwelling amplified, or compounded, detrimental effects of El Niño by increasing phytoplankton‐induced shading and mollusk grazing on juvenile and adult kelps, thereby reducing their density. Given the greater uncertainty associated with warming events and climate change in the California Current Upwelling System and its biological implications, our findings reiterate the importance of acquiring better understanding of how context‐specific underlying conditions modify ecosystem processes. More specifically, understanding how demographic traits and life history stages of kelp change with biological interactions and environmental forcing over temporal and spatial scales is crucial to anticipating future climate change ramifications.

The Canary Intermediate Poleward Undercurrent: Not Another Poleward Undercurrent in an Eastern Boundary Upwelling System

AbstractPoleward undercurrents are well-known features in eastern boundary upwelling systems. In the California Current upwelling system, the California poleward undercurrent has been widely studied, and it has been demonstrated that it transports nutrients from the equatorial waters to the northern limit of the subtropical gyre. However, in the Canary Current upwelling system, the Canary intermediate poleward undercurrent (CiPU) has not been properly characterized, despite recent studies arguing that the dynamics of the eastern Atlantic Ocean play an important role in the Atlantic meridional overturning circulation, specifically on its seasonal cycle. Here, we use trajectories of Argo floats and model simulations to characterize the CiPU, including its seasonal variability and its driving mechanism. The Argo observations show that the CiPU flows from 26°N, near Cape Bojador, to approximately 45°N, near Cape Finisterre and flows deeper than any poleward undercurrent in other eastern boundaries, with a core at a mean depth of around 1000 dbar. Model simulations manifest that the CiPU is driven by the meridional alongshore pressure gradient due to general ocean circulation and, contrary to what is observed in the other eastern boundaries, is still present at 1000 dbar as a result of the pressure gradient between the Antarctic Intermediate Waters in the south and Mediterranean Outflow waters in the north. The high seasonal variability of the CiPU, with its maximum strength in autumn and minimum in spring, is due to the poleward extension of AAIW, forced by Ekman pumping in the tropics.

Variable coastal hypoxia exposure and drivers across the southern California Current

Declining oxygen is one of the most drastic changes in the ocean, and this trend is expected to worsen under future climate change scenarios. Spatial variability in dissolved oxygen dynamics and hypoxia exposures can drive differences in vulnerabilities of coastal ecosystems and resources, but documentation of variability at regional scales is rare in open-coast systems. Using a regional collaborative network of dissolved oxygen and temperature sensors maintained by scientists and fishing cooperatives from California, USA, and Baja California, Mexico, we characterize spatial and temporal variability in dissolved oxygen and seawater temperature dynamics in kelp forest ecosystems across 13° of latitude in the productive California Current upwelling system. We find distinct latitudinal patterns of hypoxia exposure and evidence for upwelling and respiration as regional drivers of oxygen dynamics, as well as more localized effects. This regional and small-scale spatial variability in dissolved oxygen dynamics supports the use of adaptive management at local scales, and highlights the value of collaborative, large-scale coastal monitoring networks for informing effective adaptation strategies for coastal communities and fisheries in a changing climate.

Recent trends in the wind-driven California current upwelling system

Long-term changes in the marine ecosystems of the Eastern Boundary Upwelling Systems (EBUS) are predicted due to anthropogenic climate change. In particular, global ocean acidification is having a profound effect on the coastal waters of the EBUS, affecting the entire trophic chain, net primary production (NPP) and related economic activities such as fisheries. Another predicted change related to human activity is that of upwelling dynamics with expected long-term changes in upwelling winds as proposed by Bakun (1990), Bakun et al. (2015) and Rykaczewski et al. (2015). Although these predicted long-term changes may emerge only later in the 21st century, this has fueled many studies using historical data. Long-term increase in upwelling winds has thus been a much debated topic, showing that there is considerable uncertainty depending on the EBUS considered, the effect of natural climate fluctuations, the choice of wind dataset, the time period considered, and the methodologies and significance tests applied. Therefore, there is an immediate interest in being able to monitor upwelling using verified and self-consistent wind data sets. This work focused on a sensitivity study of the estimated trends in upwelling winds in the California Current Upwelling System (CCUS), for the most recent period 1996–2018, using the two state-of-the-art satellite wind analyses and two atmospheric model re-analyses. Embedded into the strong modulation by natural climate fluctuations on interannual and decadal time scales, we do see an increase in upwelling-favorable winds in the core of the CCUS, with a local increase of more than 25% in seasonal upwelling transport for the period considered. In this central upwelling zone, a good agreement on stronger equatorward winds for the winter and spring seasons is found between the different datasets, although with different significance levels. Conversely, conflicting results are found in the southernmost part of the CCUS between the satellite analyses and the model reanalyses. Systematic, time-dependent differences are found between the wind products, highlighting the need to further investigate the poorly documented temporal stability of these widely used wind long-term climatology products. The observed spatial structuring of the estimated wind trends is consistent with the trend analysis of water chlorophyll-a, partial pressure of CO2, and basity (pH) analysis products. This result is consistent with changes being important for modulating the carbonate system within the CCUS.

Synoptic forcing of wind relaxations at Pt. Conception, California

AbstractOver the California Current upwelling system in summer, the prevailing upwelling‐favorable winds episodically weaken (relax) or reverse direction for a few days. Near Pt. Conception, California, the wind usually does not reverse, but wind relaxation allows poleward oceanic coastal flow with ecological consequences. To determine the offshore extent and synoptic forcing of these wind relaxations, we formed composite averages of wind stress from the QuikSCAT satellite and atmospheric pressure from the North American Regional Reanalysis (NARR) using 67 wind relaxations during summer 2000–2009. Wind relaxations at Pt. Conception are the third stage of an event sequence that repeatedly affects the west coast of North America in summer. First, 5–7 days before the wind weakens near Pt. Conception, the wind weakens or reverses off Oregon and northern California. Second, the upwelling‐favorable wind intensifies along central California. Third, the wind relaxes at Pt. Conception, and the area of weakened winds extends poleward to northern California over 3–5 days. The NARR underestimates the wind stress within ∼200 km of coastal capes by a factor of 2. Wind relaxations at Pt. Conception are caused by offshore extension of the desert heat low. This synoptic forcing is related to event cycles that cause wind reversal as in Halliwell and Allen (1987) and Mass and Bond (1996), but includes weaker events. The wind relaxations extend ∼600 km offshore, similarly to the California‐scale hydraulic expansion fan shaping the prevailing winds, and ∼1000 km alongshore, limited by an opposing pressure gradient force at Cape Mendocino.

Experiments with Seasonal Forecasts of ocean conditions for the Northern region of the California Current upwelling system.

Resource managers at the state, federal, and tribal levels make decisions on a weekly to quarterly basis, and fishers operate on a similar timeframe. To determine the potential of a support tool for these efforts, a seasonal forecast system is experimented with here. JISAO’s Seasonal Coastal Ocean Prediction of the Ecosystem (J-SCOPE) features dynamical downscaling of regional ocean conditions in Washington and Oregon waters using a combination of a high-resolution regional model with biogeochemistry and forecasts from NOAA’s Climate Forecast System (CFS). Model performance and predictability were examined for sea surface temperature (SST), bottom temperature, bottom oxygen, pH, and aragonite saturation state through model hindcasts, reforecast, and forecast comparisons with observations. Results indicate J-SCOPE forecasts have measurable skill on seasonal timescales. Experiments suggest that seasonal forecasting of ocean conditions important for fisheries is possible with the right combination of components. Those components include regional predictability on seasonal timescales of the physical environment from a large-scale model, a high-resolution regional model with biogeochemistry that simulates seasonal conditions in hindcasts, a relationship with local stakeholders, and a real-time observational network. Multiple efforts and approaches in different regions would advance knowledge to provide additional tools to fishers and other stakeholders.

The central California Current transition zone: A broad region exhibiting evidence for iron limitation

The transition zone (TZ) of the central California Current upwelling system (cCCS) is the boundary between the cold, saline, coastally upwelled water and the warm, less saline, oligotrophic waters of the offshore California Current (CC). The TZ is a broad region that regularly exhibits chlorophyll concentrations of 1–2μgL−1 throughout the spring, summer, and fall seasons. Surface transect and vertical profile data from three cruises (May 2010, June 1999, and August 2011) between 34 and 42°N show residual nitrate concentrations (5–15μM) and low Fe concentrations (most<0.2nmolkg−1) in the TZ. We therefore suggest that much of the TZ of the cCCS is an Fe-limited, high nutrient, lower than expected chlorophyll (HNLC) region. The main source of Fe to the cCCS is from upwelling through the benthic boundary layer (BBL) over the continental shelf sediments. Iron and NO3- in coastally upwelled water are transported via offshore moving filaments into the TZ. However, since some coastal upwelling regions with narrow continental shelves do not have much Fe to begin with, and since Fe is drawn down more rapidly relative to NO3- due to biological assimilation and scavenging, these filaments transport low concentrations of Fe relative to NO3- into the TZ. Weak wind curl-induced upwelling and vertical mixing in the TZ also deliver Fe and NO3- to the surface but at lower concentrations (and lower Fe:NO3-) than from strong coastal upwelling. Mesoscale cyclonic eddies in the TZ are important to consider with respect to offshore surface nutrient delivery because there is a marked shoaling of isopycnals and the nutricline within these eddies allowing higher nutrient concentrations to be closer to the surface. Since wind curl-induced upwelling and/or vertical mixing occurs seaward of the continental shelf, there is not enough Fe delivered to the surface to accompany the NO3-. By using Fe:NO3- ratios and calculated specific growth rates for diatoms, we demonstrate that the TZ of the cCCS shows evidence for Fe limitation of diatom blooms. The TZ also appears to progress further into Fe limitation as the upwelling season progresses from spring into late summer. This study provides some of the first field data to suggest that Fe is a critical bottom up control on the ecosystem in the TZ of the cCCS.

Air–sea exchange of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; at a Northern California coastal site along the California Current upwelling system

Abstract. It is not well understood whether coastal upwelling is a net CO2 source to the atmosphere or a net CO2 sink to the ocean due to high temporal variability of air–sea CO2 exchange (CO2 flux) in coastal upwelling zones. Upwelling transports heterotrophic, CO2 enriched water to the surface and releases CO2 to the atmosphere, whereas the presence of nutrient-rich water at the surface supports high primary production and atmospheric CO2 uptake. To quantify the effects of upwelling on CO2 flux, we measured CO2 flux at a coastal upwelling site off of Bodega Bay, California, with the eddy covariance technique during the summer of 2007 and the fall of 2008, and the bulk method with partial pressure of CO2 of surface water (pCO2) data from November 2010 to July 2011. Variations in sea surface temperatures (SST) and alongshore wind velocity suggest that the measurement period in 2007 coincided with a typical early summer upwelling period and the measurement period in 2008 was during a typical fall relaxation period. A strong source of CO2 (~ 1.5 ± 7 SD (standard deviation) g C m−2 day−1) from the ocean to the atmosphere during the upwelling period was concurrent with high salinity, low SST, and low chlorophyll density. In contrast, a weak source of CO2 flux (~ 0.2 ± 3 SD g C m−2 day−1) was observed with low salinity, high SST and high chlorophyll density during the relaxation period. Similarly, the sink and source balance of CO2 flux was highly related to salinity and SST during the pCO2 measurement periods; high salinity and low SST corresponded to high pCO2, and vice versa. We estimated that the coastal area off Bodega Bay was likely an overall source of CO2 to the atmosphere based on the following conclusions: (1) the overall CO2 flux estimated from both eddy covariance and pCO2 measurements showed a source of CO2; (2) although the relaxation period during the 2008 measurements were favorable to CO2 uptake, CO2 flux during this period was still a slight source; (3) salinity and SST were found to be good predictors of the CO2 flux for both eddy covariance and pCO2 measurements, and 99% of the historical SST and salinity data available between 1988 and 2011 fell within the range of our observations in May–June 2007, August–September 2008 and November 2010–July~2011, which indicates that our data set was representative of the annual variations in the sea state. Based on the developed relationship between pCO2, SST and salinity, the study area between 1988 and 2011 was estimated to be an annual source of CO2 of ~ 35 mol C m−2 yr−1. The peak monthly CO2 flux of ~ 7 mol C m−2 month−1 accounted for almost 30% of the dissolved inorganic carbon in the surface mixed layer.

Contrasting effects of hypoxic conditions on survivorship of planktonic larvae of rocky intertidal invertebrates

Hypoxia is increasing in coastal zones worldwide, with acute effects on demersal fish and benthic invertebrate communities in shallow coastal and estuarine habitats. Less studied are the effects of hypoxia on planktonic larvae of open coastal habitats. Climate change projections suggest intensified hypoxia in open coast upwelling systems, such as the northern California Current Upwelling System, where there has been a recent rise of seasonally persistent inner-shelf hypoxia (dissolved oxygen (DO) < 1.43 ml l �1 ) and anoxia (DO 0 ml l �1 ). We examined survivorship of larval invertebrates exposed to low oxygen conditions in controlled laboratory experiments. Multiple-day hypoxic conditions, resembling DO levels in nearshore Oregon waters, were gene - rated by bubbling seawater with nitrogen gas. Tolerance levels among species varied, from larvae of species with little tolerance to hypoxia (e.g. the shore crab Hemigrapsus oregonensis) to species with high tolerance (e.g. the California mussel Mytilus californianus). These contrasting responses among open-coast intertidal taxa suggest that chronic hypoxia or anoxia may have different effects on recruitment success among species and, consequently, on the structure and species composition of open coast intertidal communities.

Correction to “North Pacific Gyre Oscillation modulates seasonal timing and ecosystem functioning in the California Current upwelling system”

[1] In the paper “North Pacific Gyre Oscillation modulates seasonal timing and ecosystem functioning in the California Current upwelling system, ” by F. Chenillat et al. (Geophysical Research Letters, 39, L01606, doi:10.1029/ 2011GL049966, 2012), Figure 4b is modified without change to the caption: black and white dots (averaged Chl-a CalCOFI data) were erroneous. The second sentence of paragraph 17 is changed in consequence to “General patterns of the twin simulations are in agreement with the main characteristics of the dynamics of the CCS (Figure 4b), albeit with a high Chl-a bias nearshore.”

Interannual variability in bottom-up processes in the upstream range of the California Current system: An isotopic approach

The abundance and composition of zooplankton, fish and seabirds show dramatic interannual variability in temperate coastal regions. Understanding links between this variability and bottom-up processes is an important goal for biological oceanographers. Because zooplankton stable isotopes (δ15N and δ13C) are potentially influenced by variability in phytoplankton nutrient utilization, primary production, and zooplankton trophic structure, they have the potential to elucidate links between bottom-up processes, food web structure, and abundance or species composition of higher trophic levels. Here we measure correlations between zooplankton stable isotopes and oceanographic variables in two time series from the west coast of Vancouver Island, upstream of the California Current upwelling system. We then relate interannual variability in zooplankton stable isotopes to interannual variability in zooplankton species composition. Zooplankton stable isotopes show striking patterns of seasonal, regional and interannual variability. A strong positive correlation between annual averages of zooplankton δ15N and sea-surface temperature is evident in both time series. Zooplankton δ15N is also negatively correlated with interannual anomalies of subarctic copepod biomass in both time series. We propose two different mechanisms to explain these correlations: variability in the strength and direction of horizontal advection, or local fluctuations nutrient availability. We conclude that they are most likely caused by local, temperature-driven fluctuations in nitrate concentrations and primary production. We show that the positive correlation between zooplankton δ15N and temperature is widespread, extending to regions outside of the California Current system. Our findings suggest that interannual variability in zooplankton composition is linked with bottom-up variability in nitrate availability and primary production in the upstream portion of the California Current system. Our results also highlight the potential of integrating biochemical parameters in zooplankton time series for elucidating links between bottom-up processes and the survival of higher trophic levels in the ocean.

North Pacific Gyre Oscillation modulates seasonal timing and ecosystem functioning in the California Current upwelling system

On interannual and longer time scales, dynamical and biogeochemical fluctuations in the North Pacific are dominated by two modes of variability, namely the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation (NPGO). In this study the regional expression of the NPGO in the California Current System (CCS) is detailed. The statistical relationship between the NPGO index and nearshore wind variability (mostly upwelling favorable) along the U.S. West coast is strongest in the wintertime (December to March) off Central California. Most importantly, NPGO fluctuations are associated with a seasonal shift of 1–2 months in the onset of the upwelling season. Regional numerical simulations show that an early (late) onset of upwelling during the positive (negative) phase of the NPGO leads to a more (less) productive planktonic ecosystem throughout spring and summer, i.e., several months after the direct NPGO effects on the system have ceased. These results bring new light on the California ecosystem variability as observed in atypical years such as 2005 and 2007.

Epipelagic fish distributions in relation to thermal fronts in a coastal upwelling system using high-resolution remote-sensing techniques

Abstract Reese, D. C., O'Malley, R. T., Brodeur, R. D., and Churnside, J. H. 2011. Epipelagic fish distributions in relation to thermal fronts in a coastal upwelling system using high-resolution remote-sensing techniques. – ICES Journal of Marine Science, 68: 1865–1874. Coastal upwelling systems are characterized by substantial spatial and temporal variability with respect to surface conditions, with fauna patchily distributed and high abundances in localized areas. Examining habitat associations on finer spatial scales than previous studies have been able to achieve would advance the understanding of important marine coastal ecosystems. This study evaluates the spatial and temporal relationships of single fish and fish schools with sea surface temperature (SST) fronts in the northern California Current upwelling system, using lidar (light detection and ranging) from an aircraft to sample surface waters over the continental shelf. High-resolution data were collected on the distribution of surface nekton and SST, then the locations of fish were analysed with respect to their proximity to SST fronts using GIS spatial analyses. Both fish schools and solitary fish were located significantly closer to fronts than would be expected by chance. The association of fish to fronts varied with the progression of the upwelling season such that fish associated less with fronts under stronger upwelling conditions. The relationships observed indicate the importance of thermal features to fish as a habitat component in a variable upwelling environment and have implications for management and conservation.

Recurrent frontal slicks of a coastal ocean upwelling shadow

Marine ecosystems are greatly influenced by the structure and dynamics of fronts. In coastal upwelling systems, frontogenesis occurs frequently by upwelling and transport of cold water and warming in sheltered “upwelling shadow” retention sites. Monterey Bay, in the California Current upwelling system, hosts a dynamic upwelling shadow environment. Using a decade of satellite synthetic aperture radar (SAR) observations with ancillary remote sensing and in situ data, we describe recurrent surface slicks that develop along the seaward periphery of the Monterey Bay upwelling shadow, and we examine their relationships with fronts. Slick median dimensions, 17.5 km long and 0.8 km wide, describe their elongated structure. Although the typical pattern is a single slick, multiple slicks may concurrently develop in association with different types of fronts. Repeated volume surveys through a front, underlying a slick, revealed lateral mixing and interleaving of regional water types. Velocity fields from coastal HF radar show that slicks may coincide with a variety of surface circulation patterns, that they may extend contiguously across regions having very different surface velocity, and that they may be separated from the shear front of upwelling filaments by 5–10 km. Slicks occur in all seasons and may coincide with both upwelling and downwelling wind forcing. Surfactant accumulation in small‐scale convergence zones is indicated as the primary mechanism of slick formation, not ocean current shear or small‐scale air‐sea coupling. The results of this study emphasize the role of upwelling system fronts in creating small‐scale structure and dynamics that influence plankton ecology.

Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs

Systematic monitoring of seabird populations in Canada has been ongoing since the 1920s and the monitoring of diets and other biological indicators of ecosystem change started in the 1970s. Long-term monitoring of population parameters began in the 1980s. These studies originally were conducted mainly by the Canadian Wildlife Service, but subsequently have involved several universities and nongovernment organization groups. We review the results of this monitoring from the 1970s onwards for six oceanographic regions to assess population trends among Canadian seabirds and correlated trends in diets, phenology, and other breeding biology variables. Within regions, trends in most variables studied have been broadly congruent, but there was often variation among regions. In particular, seabird populations in the Pacific coast zone affected by the California Current upwelling system have shown generally negative trends since the 1980s, whereas trends for populations of the same species to the north of this zone have been mainly positive. Likewise, on the east coast, trends at Arctic colonies have been decoupled from those at colonies around Newfoundland and in the Gulf of St. Lawrence, especially since the major cold water event of the early 1990s. Several long-term studies have shown an association between population events and diet and phenology changes. Diet and indicators of condition (chick growth, reproductive success) sometimes responded very rapidly to oceanic changes, making them excellent signals of ecosystem perturbations. The review highlights the effects of decadal-scale regime shifts on Canadian seabirds, confirms the value of long-term studies and supports the applicability of single-site observations to regional populations.

Issues of ecosystem-based management of forage fisheries in “open” non-stationary ecosystems: the example of the sardine fishery in the Gulf of California

The Gulf of California system presents major challenges to the still developing frameworks for ecosystem-based management (EBM). It is very much an open system and is intermittently subject to important influxes of migratory visitors, including large pelagic predatory fishes and small pelagic forage fishes. These migrants include the more tropical species from the coastal ecosystems to the south and perhaps subtropical sardines and anchovies from the California Current upwelling system. In addition to the multi-annual ENSO-scale and what may seem to be rather erratic episodes of major population incursions, the Gulf presents nonstationary, transient aspects on a variety of longer time scales. Moreover, the removal of top predators by commercial and sport fisheries has introduced trends that must be affecting the entire ecosystem, and certainly the forage fishes that are their major prey base. In addition to size limits, fishing seasons, area closures and license limitations, the fishery is managed by an ad hoc adaptive management system, in which the fishing season can be shortened or additional areas closed to fishing if pre-season exploratory fishing surveys indicate a shortage of small pelagic fishes on the fishing grounds. Whether this system is likely to be sustainable in the long term is difficult to determine, given the potential for rapid changes in the system because of environmental changes and/or feedbacks within the food web. Thus it appears that innovative management frameworks, among other things utilizing the comparative method, may be required in order to determine defensible tradeoffs between precaution and resource utilization.

Carbon monoxide and chromophoric dissolved organic matter cycles in the shelf waters of the northern California upwelling system

An annual program of approximately bimonthly seawater sampling was conducted off the coast of the Bodega Marine Laboratory in the California Current upwelling system (CCUS) to investigate controls on dissolved carbon monoxide (CO) and its photochemical parent, chromophoric dissolved organic matter (CDOM). A diel steady state model was developed to quantify CO sources and sinks throughout the day. Observed midday CO spanned 2.7–17 nmol L−1, and correlated strongly with coincident CDOM absorption; however, rapid microbial consumption rates (0.05–0.80 h−1) were such that ∼95% of the CO generated was metabolized within the ocean surface. Further indication of the dominant influence of the microbial ecosystem was the persistent observation of a strong “dark production,” which contributed ∼25% of the diurnal source strength within the top 17 m of the ocean. The dark source correlated strongly with biological oxidation rates and CDOM, suggesting that it is the result of incomplete respiration of biologically labile DOM. CDOM was lowest in recently upwelled waters, implying that its origin is from the induced primary production and not from shelf sediment resuspension. The estimated CO air‐sea flux was highly variable (average of 5 μmol m−2 d−1), and most likely inconsequential to the atmospheric budget in coastal regions. The photolytic source strength of CO2 from CDOM (2.7 mmol m−2 d−1) was estimated by scaling to modeled CO photoproduction rates. This photolytic remineralization rate represents ∼2.5% of the net primary production in the CCUS, implying that CDOM photobleaching may play a significant role in the carbon cycling of upwelling systems.