Burke Hales

Evidence for Upwelling of Corrosive Acidified Water onto the Continental Shelf

The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of ∼40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area.

Limacina helicina shell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem

Few studies to date have demonstrated widespread biological impacts of ocean acidification (OA) under conditions currently found in the natural environment. From a combined survey of physical and chemical water properties and biological sampling along the Washington–Oregon–California coast in August 2011, we show that large portions of the shelf waters are corrosive to pteropods in the natural environment. We show a strong positive correlation between the proportion of pteropod individuals with severe shell dissolution damage and the percentage of undersaturated water in the top 100 m with respect to aragonite. We found 53% of onshore individuals and 24% of offshore individuals on average to have severe dissolution damage. Relative to pre-industrial CO2 concentrations, the extent of undersaturated waters in the top 100 m of the water column has increased over sixfold along the California Current Ecosystem (CCE). We estimate that the incidence of severe pteropod shell dissolution owing to anthropogenic OA has doubled in near shore habitats since pre-industrial conditions across this region and is on track to triple by 2050. These results demonstrate that habitat suitability for pteropods in the coastal CCE is declining. The observed impacts represent a baseline for future observations towards understanding broader scale OA effects.

Iron links river runoff and shelf width to phytoplankton biomass along the U.S. West Coast

A poleward increase in phytoplankton biomass along the West Coast of North America has been attributed to increasing river runoff towards the north. We combine streamflow and shelf width data with satellite-derived estimates of phytoplankton biomass to quantify the relationship between these variables. We find that a combination of winter streamflow and shelf width can account for over 80% of the spatial variance in summer chlorophyll within 50 km of the coast. At a given location, interannual variability in streamflow is not associated with interannual variability in chlorophyll. We attribute these relationships to the role of rivers as suppliers of the micronutrient iron, and the role of the shelf as a ‘capacitor’ for riverine iron, charging during the high-flow winter season and discharging during the upwelling season. Data from the Oregon shelf confirm that, during winter, a significant fraction of riverine iron escapes the estuary and reaches the coastal ocean.

Ocean Acidification Has Multiple Modes of Action on Bivalve Larvae.

Ocean acidification (OA) is altering the chemistry of the world’s oceans at rates unparalleled in the past roughly 1 million years. Understanding the impacts of this rapid change in baseline carbonate chemistry on marine organisms needs a precise, mechanistic understanding of physiological responses to carbonate chemistry. Recent experimental work has shown shell development and growth in some bivalve larvae, have direct sensitivities to calcium carbonate saturation state that is not modulated through organismal acid-base chemistry. To understand different modes of action of OA on bivalve larvae, we experimentally tested how pH, PCO2, and saturation state independently affect shell growth and development, respiration rate, and initiation of feeding in Mytilus californianus embryos and larvae. We found, as documented in other bivalve larvae, that shell development and growth were affected by aragonite saturation state, and not by pH or PCO2. Respiration rate was elevated under very low pH (~7.4) with no change between pH of ~ 8.3 to ~7.8. Initiation of feeding appeared to be most sensitive to PCO2, and possibly minor response to pH under elevated PCO2. Although different components of physiology responded to different carbonate system variables, the inability to normally develop a shell due to lower saturation state precludes pH or PCO2 effects later in the life history. However, saturation state effects during early shell development will carry-over to later stages, where pH or PCO2 effects can compound OA effects on bivalve larvae. Our findings suggest OA may be a multi-stressor unto itself. Shell development and growth of the native mussel, M. californianus, was indistinguishable from the Mediterranean mussel, Mytilus galloprovincialis, collected from the southern U.S. Pacific coast, an area not subjected to seasonal upwelling. The concordance in responses suggests a fundamental OA bottleneck during development of the first shell material affected only by saturation state.

Southern Ocean Gas Exchange Experiment: Setting the stage

[1] The Southern Ocean Gas Exchange Experiment (SO GasEx) is the third in a series of U.S.‐led open ocean process studies aimed at improving the quantification of gas transfer velocities and air‐sea CO2 fluxes. Two deliberate 3He/SF6 tracer releases into relatively stable water masses selected for large DpCO2 took place in the southwest Atlantic sector of the Southern Ocean in austral fall of 2008. The tracer patches were sampled in a Lagrangian manner, using observations from discrete CTD/Rosette casts, continuous surface ocean and atmospheric monitoring, and autonomous drifting instruments to study the evolution of chemical and biological properties over the course of the experiment. CO2 and DMS fluxes were directly measured in the marine air boundary layer with micrometeorological techniques, and physical, chemical, and biological processes controlling air‐sea fluxes were quantified with measurements in the upper ocean and marine air. Average wind speeds of 9 m s−1 to a maximum of 16 m s−1 were encountered during the tracer patch observations, providing additional data to constrain wind speed/gas exchange parameterizations. In this paper, we set the stage for the experiment by detailing the hydrographic observations during the site surveys and tracer patch occupations that form the underpinning of observations presented in the SO GasEx special section. Particular consideration is given to the mixed layer depth as this is a critical variable for estimates of fluxes and biogeochemical transformations based on mixed layer budgets.

Ocean deoxygenation: Past, present, and future

To a first order, the oxygen content of the ocean interior is determined by the influx of the gas across the air-sea surface (i.e., ventilation) and consumption due primarily to microbial respiration. As these two competing processes vary in space and time, so does the concentration of oxygen in the ocean interior. Although oxygen concentrations on continental margins are declining in many regions due to increased anthropogenic nutrient loadings [e.g., Rabalais et al., 2002], oxygen also appears to be declining in both the central North Pacific Ocean and the tropical oceans worldwide [Emerson et al., 2004; Whitney et al., 2007; Keeling et al., 2010] (see Figure 1). It is unclear whether the loss throughout the basins in the open ocean is a long-term, nonperiodic (secular) trend related to climate change, the result of natural cyclical processes, or a combination of both (Figure 2). If related to climate change, a number of important factors may be involved, including decreased solubility of oxygen as waters warm, decreased ventilation at high latitudes associated with increased ocean stratification, and changes in respiration in the ocean interior.

Distribution and variability of iron input to Oregon coastal waters during the upwelling season

generally higher in spring (mean of 2.1 and 33.9 nmol L 1 , respectively) than in summer (means of 1.4 and 15.4 nmol L 1 ). In spring and summer, high iron concentrations in surface waters were associated with both cold and saline, recently upwelled waters, and with fresh, relatively warm water influenced by the Columbia River. Comparison of total dissolvable iron in 0.45 mm filtered and in unfiltered samples indicated a substantial contribution from particulate iron. Iron concentrations in summer were generally lower than in spring throughout the water column, with the exception of the near-bottom, where concentrations were generally higher in summer than spring. Optical backscatter data from moored sensors were used to infer the vertical and cross-shelf transport of iron-bearing particles during the upwelling season over a steep shelf. Cross-correlation analysis showed downslope movement of particles from the deep inner shelf to the deep midshelf. There was also evidence for sinking of biogenic particles at the midshelf and inner shelf, but we found no evidence of upslope transport of benthic particles. Sufficient iron is available in this system to meet the demands of the phytoplankton, which are able to make full use of available nitrate. Citation: Chase, Z., B. Hales, T. J. Cowles, R. Schwartz, and A. van Green (2005), Distribution and variability of iron input to Oregon coastal waters during the upwelling season, J. Geophys. Res., 110, C10S12, doi:10.1029/2004JC002590.

High-resolution biogeochemical investigation of the Ross Sea, Antarctica, during the AESOPS (U. S. JGOFS) Program

[1] The results of high-resolution biogeochemical measurements in the upper 200 m of the Ross Sea, Antarctica, obtained during the AESOPS (U. S. JGOFS) program using the Lamont Pumping SeaSoar (LPS) are presented. They consist of three west-east transects from 170� E to 180� longitude along the AESOPS study line at 76.5� S and three short north-south transects in the Ross Sea polynya during the initial and maturing stages of phytoplankton blooms in the austral spring and early summer of 1997. The LPS carried an in situ instrument array for measurement of temperature, salinity, fluorescence, photosynthetically active radiation (PAR), and dissolved oxygen. In addition, a highpressure pump mounted aboard the LPS fish delivered a continuous seawater sample stream to the shipboard laboratory for high-speed analysis of its nutrient (nitrate plus nitrate, phosphate, and silicate) and total CO2 concentrations and CO2 partial pressure (PCO2). Vertical resolution of this sampling equaled or exceeded that of hydrostation-style conductivity-temperature-depth (CTD) casts; horizontal resolution (nominally equal to a vertical cast every 3–5 km) exceeded station resolution by a factor of 10. While not perfectly synoptic, the 20-hour duration of these transects is far shorter than the time typically taken to complete the line with conventional sampling methods. These surveys clearly identified three distinct deep water masses below about 100 m: High-Salinity Shelf Water (HSSW) in the western end of the transects, Modified Circumpolar Deep Water (MCDW) in the middle of the transects, and Low-Salinity Shelf Water (LSSW) to the east. The regions to the west were characterized by high biological productivity with high N:P and C:P uptake ratios, but little Si uptake, indicating that the production was dominated by Phaeocystis. To the east, biological productivity was lower than in the west, and low N:P and C:P uptake ratios and high Si uptake indicated the dominance of diatoms. The difference in uptake ratios appears to be entirely due to anomalously high P uptake by diatoms; N:C uptake ratios are similar in the two regions and very near canonical Redfield stoichiometry. The area in the center of the transects was characterized by high stratification and low, diatom-dominated productivity; the reason for this low productivity is unclear but is speculated to be due to the short time which this water has been exposed to an ice-free surface. The presence of strong variability at horizontal length scales of order 10 km is evident in nearly all fields especially in upper 100 m, although many of the features are resolved only by two or three LPS tracks (each separated by only a few kilometers). Physical, bio-optical, and chemical variability is observed to extend vertically from sea surface to depths as deep as 140 m far below the 1% light level and the mixed layer depth. This may be attributed to downwelling of waters associated with eddies and/or meandering. A simple statistical measure presented to quantify the errors associated with the undersampling of such a highly variable field shows that biogeochemically important parameters like PCO2 and oxygen and chlorophyll concentrations are poorly resolved by a commonly used 50-km hydro-station spacing. Longitudinal averages of these parameters, however, are predicted fairly well at coarser resolutions. INDEX TERMS: 4207 Oceanography: General: Arctic and Antarctic oceanography; 4805

The Pumping SeaSoar: A High-Resolution Seawater Sampling Platform

Abstract The first results obtained with the Lamont Pumping SeaSoar (LPS), a combination measurement and sampling platform towed by a research ship at speeds of 6–7 kt, are presented. The system allows not only measurement of a suite of oceanographic parameters with in situ sensors, but also delivery of seawater samples through a 750-m tube (5/16-in. inner diameter) to a shipboard laboratory for chemical analyses, while undulating from near the surface to depths near 200 m. Here the performance of the system is demonstrated, and the time lag and signal smearing associated with the seawater sampling scheme are qualitively analyzed. The time lag was determined by comparing salinity determined from measurements of temperature, conductivity, and pressure made in situ by the sensors mounted on the towed body, with salinity determined from temperature and conductivity measurements made in the shipboard outlet of the sample stream. It varied smoothly from 10.8 to 11.5 min over 24 h of sampling, independent of th...

Distributions and Variability of Particulate Organic Matter in a Coastal Upwelling System

[1] In this study we examined the spatial and temporal variability of particulate organic material (POM) off Oregon during the upwelling season. High-resolution vertical profiling of beam attenuation was conducted along two cross-shelf transects. One transect was located in a region where the shelf is relatively uniform and narrow (off Cascade Head (CH)); the second transect was located in a region where the shelf is shallow and wide (off Cape Perpetua (CP)). In addition, water samples were collected for direct analysis of chlorophyll, particulate organic carbon (POC), and particulate organic nitrogen (PON). Beam attenuation was highly correlated with POC and PON. Striking differences in distribution patterns and characteristics of POM were observed between CH and CP. Off CH, elevated concentrations of chlorophyll and POC were restricted to the inner shelf and were highly variable in time. The magnitude of the observed short-term temporal variability was of the same order as that of the seasonal variability reported in previous studies. Elevated concentrations of nondegraded chlorophyll and POM were observed near the bottom. Downwelling and rapid sinking are two mechanisms by which phytoplankton cells can be delivered to the bottom before being degraded. POM may be then transported across the shelf via the benthic nepheloid layer. Along the CP transect, concentrations of POM were generally higher than they were along the CH transect and extended farther across the shelf. Characteristics of surface POM, namely, C:N ratios and carbon:chlorophyll ratios, differed between the two sites. These differences can be attributed to differences in shelf circulation. INDEX TERMS: 4279 Oceanography: General: Upwelling and convergences; 4219 Oceanography: General: Continental shelf processes; 4805 Oceanography: Biological and Chemical: Biogeochemical cycles (1615); KEYWORDS: POM, upwelling, beam attenuation