Central California Current System Research Articles

Coastal iron and nitrate distributions during the spring and summer upwelling season in the central California Current upwelling regime

Distributions of iron and nitrate in the central California Current System upwelling regime (cCCS) from 34 to 41°N were determined during cruises in May 2010 and August 2011. High spatial and temporal resolution data for dissolved Fe and NO3− (nitrate+nitrite) in the cCCS from this study greatly expands upon previous studies that were narrower in scope (e.g., focused on just the Monterey Bay region). Shelf sediments from mid-shelf mud belts in this region provide the dominant source of Fe, and there are areas in the cCCS where insufficient Fe is upwelled to accompany elevated levels of other macronutrients (nitrate, phosphate, silicate) to fuel extensive diatom blooms. Surface dissolved Fe concentrations were related to continental shelf width and upwelling strength, and surface Fe concentrations tended to be lower in the late summer than early spring. We present extensive benthic boundary layer (BBL) dissolved and leachable particulate Fe data from both seasons in the mid-shelf region along the central California coast. Leachable particulate Fe concentrations were strongly related to the width of the mid-shelf mud belts (i.e., the continental shelf between the 50 and 90m isobaths). Dissolved Fe concentrations in the BBL over the mid-shelf were generally highest in wide mud belt areas as well as in areas with very low dissolved oxygen concentrations but did not show a clear seasonal trend. Evidence for probable Fe limitation in upwelled waters was found by using surface dissolved Fe:NO3− ratios and the estimated specific growth rate of coastal diatoms based on either Fe or NO3− concentrations. Several coastal upwelling regions with only moderate to narrow continental shelves (Pt. Arena to Cape Mendocino and the Big Sur Coast) exhibited evidence for Fe limitation in both the spring and summer upwelling seasons.

Sources and distributions of Mn, Fe, Co, Ni, Cu, Zn, and Cd relative to macronutrients along the central California coast during the spring and summer upwelling season

Coastal upwelling in the central California Current System (cCCS) delivers macro and micronutrients to the surface ocean that fuel biological productivity. Variations in upwelling strength and continental shelf width affect trace metal sources seasonally. The purpose of this study was to investigate various sources and distributions for a suite of dissolved trace metals (Mn, Fe, Co, Ni, Cu, Zn, and Cd) in the cCCS (34–41°N) as well as to determine the effects of biological uptake, physical advection, and mixing processes on trace metal concentrations during the spring and summer upwelling season. Continental shelf sediments did not substantially affect upwelled concentrations of Ni, Zn, and Cd — three typical nutrient-type trace metals. However, shelf sediments provided a significant external source for Mn, Fe, Co, and Cu — scavenged and hybrid-type trace metals. There was no clear seasonal trend in benthic boundary layer (BBL) Fe concentrations; however, higher concentrations of Mn and Co together with lower O2 concentrations were found in the BBL in the late summer compared to early spring. Conversely, there was a higher sedimentary Cu source to the BBL in the early spring before O2 concentrations dropped. Surface transect samples along the Big Sur Coast (May, 2010) and North Coast (August, 2011) demonstrated both mixing and biological assimilation of NO3− and trace metals. Iron and Zn showed accelerated drawdown relative to NO3− during both seasons suggesting an increased metal to nitrogen drawdown ratio at higher dissolved metal concentrations. Surface Mn and Co concentrations were higher in the late summer and both showed evidence for accelerated drawdown relative to NO3−. Cadmium and Ni were strongly correlated with NO3− indicating that both are affected by a combination of assimilation and regeneration at a constant rate relative to NO3−; however, Cd showed slightly increased drawdown in aged upwelled waters during the late summer when Zn and Fe concentrations were low. This study provides field trace metal and macronutrient data supporting past laboratory studies suggesting that complex biological interactions are a key control on trace metal distributions and marine biogeochemical cycles.

Spatiotemporal variability and long-term trends of ocean acidification in the California Current System

Abstract. Due to seasonal upwelling, the upper ocean waters of the California Current System (CCS) have a naturally low pH and aragonite saturation state (Ωarag), making this region particularly prone to the effects of ocean acidification. Here, we use the Regional Oceanic Modeling System (ROMS) to conduct preindustrial and transient (1995–2050) simulations of ocean biogeochemistry in the CCS. The transient simulations were forced with increasing atmospheric pCO2 and increasing oceanic dissolved inorganic carbon concentrations at the lateral boundaries, as projected by the NCAR CSM 1.4 model for the IPCC SRES A2 scenario. Our results show a large seasonal variability in pH (range of ~ 0.14) and Ωarag (~ 0.2) for the nearshore areas (50 km from shore). This variability is created by the interplay of physical and biogeochemical processes. Despite this large variability, we find that present-day pH and Ωarag have already moved outside of their simulated preindustrial variability envelopes (defined by ±1 temporal standard deviation) due to the rapidly increasing concentrations of atmospheric CO2. The nearshore surface pH of the northern and central CCS are simulated to move outside of their present-day variability envelopes by the mid-2040s and late 2030s, respectively. This transition may occur even earlier for nearshore surface Ωarag, which is projected to depart from its present-day variability envelope by the early- to mid-2030s. The aragonite saturation horizon of the central CCS is projected to shoal into the upper 75 m within the next 25 yr, causing near-permanent undersaturation in subsurface waters. Due to the model's overestimation of Ωarag, this transition may occur even earlier than simulated by the model. Overall, our study shows that the CCS joins the Arctic and Southern oceans as one of only a few known ocean regions presently approaching the dual threshold of widespread and near-permanent undersaturation with respect to aragonite and a departure from its variability envelope. In these regions, organisms may be forced to rapidly adjust to conditions that are both inherently chemically challenging and also substantially different from past conditions.

Marine mammal occurrence and ocean climate off central California, 1986 to 1994 and 1997 to 1999

The California Current System (CCS), a highly variable eastern boundary system, sup- ports a rich marine mammal fauna. Variation in local coastal upwelling, coupled with larger scale processes (El Nino/La Nina) affects the productivity and distribution of marine species at all trophic levels. Herein, we present an analysis of the occurrence patterns of marine mammals in the central CCS and relate these patterns to changing ocean climate and prey availability. Data on marine mammal distributions, ocean conditions, and prey availability were collected in waters overlying the continental shelf and slope from Bodega to Monterey Bays, from 1986 to 1994 and 1997 to 1999. Occurrence patterns were investigated using geographical information system (GIS), percent simi- larity index (PSI), multiple logistic regression, and principal component analyses. Spatial patterns of the most frequently sighted species (California sea lion Zalophus californianus, northern fur seal Callorhinus ursinus, Pacific white-sided dolphin Lagenorhyncus obliquidens, Dall's porpoise Pho- coenoides dalli, harbor porpoise Phocoena phocoena,and humpback whale Megaptera novaean- gliae) were related to bathymetry and changing ocean climate, and were likely to have been medi- ated by changes in prey availability. Temporal changes were related to migration and significant differences in ocean structure resulting from both local and large-scale processes.

Ocean climate, euphausiids and auklet nesting: inter-annual trends and variation in phenology, diet and growth of a planktivorous seabird, Ptychoramphus aleuticus

Variability in ocean climate results in fluctuations in the timing and abundance of zoo- plankton. In turn, fluctuations in zooplankton as prey may have consequences for reproductive deci- sions and performance of planktivorous seabirds. We examined interrelationships between mean sea- sonal oceanographic conditions and prey availability and the timing of breeding, nestling diet, growth and productivity (as number of chicks fledged per breeding pair) of Cassin's auklet Ptychoramphus aleuticus in the central California Current System. Substantial inter-annual variability in seasonal ocean climate parameters as well as in auklet reproductive and diet characteristics was evident. Hatching dates and the proportion of all euphausiids in the diet were positively correlated with sea- sonal sea-surface temperature and negatively correlated with seasonal upwelling values. A significant negative correlation was found between the proportion of Euphausia pacifica in the diet and hatch date, while significant positive correlations were found between Thysanoessa spinifera in the diet and productivity, and between productivity and growth. Based on the California Cooperative Fisheries In- vestigations euphausiid data set, significant positive correlations were found between E. pacifica abundance and auklet meal mass and productivity and between T. spinifera abundance and auklet productivity. As demonstrated by the auklet diet, euphausiids responded to changes in ocean climate on multiple temporal scales. In most years, auklets responded adaptively to variation in oceanographic conditions and prey availability by modifying timing of breeding. However, in years when ocean con- ditions deteriorated after the initiation of breeding, prey availability was severely reduced beyond the auklet's adaptive response, resulting in diminished nestling growth and productivity.

Geomagnetic map used for long-distance navigation?

We used stable isotopes (δ15N and δ13C) and compared prey provided to chicks by each sex to evaluate seasonal and sex-specific diets in Rhinoceros Auklets (Cerorhinca monocerata) in the central California Current system during 2012–2013. Mixing models indicated northern anchovy (Engraulis mordax) were important prey for adults during fall/winter and juvenile rockfishes (Sebastes spp.) were important prey during incubation both years. Adult trophic level increased between incubation and chick-rearing periods in both years. During 2012, δ15N and δ13C of chick-rearing males and females differed significantly; mixing models indicated that females ate more Pacific saury (Cololabis saira) and less market squid (Doryteuthis opalescens) than males. Likewise, females delivered significantly more Pacific saury and less market squid to chicks than males during 2012. Chick growth (g d− 1) and chick survival to fledging were significantly lower during 2012 than 2013, likely because chicks were fed lesser quality prey or fed less frequently in 2012. Lesser body mass of females during incubation in 2012 indicated sex-specific diet differences may have been related to female energetic constraints. The observed variability in Rhinoceros Auklet diet underscores the importance of managing multiple prey populations in this system so that generalist predators have sufficient resources through changing conditions.