Sea-air CO₂ flux variability on the northeast Pacific continental margin

Carbon dioxide (CO₂) fluxes between the ocean and atmosphere on continental margins are difficult to diagnose because these regions experience large variability over spatial and temporal scales spanning meters to basins and hours to years, respectively. In a global sense, continental margins could represent a significant atmospheric CO₂ sink, equivalent to ~30% of the open ocean CO₂ uptake. However, many regions have inadequate data coverage to resolve the large inherent variability. The role of continental margins also becomes increasingly more complicated if nearshore waters, such as estuaries and salt marshes, are included in global or regional carbon budgets. This thesis addresses variability in surface seawater CO₂ partial pressure (pCO₂) and sea-air CO₂ flux across three sub-regions of the northeast Pacific continental margin: the Oregon shelf, the western Canadian coastal ocean, and the Columbia River Estuary and plume. Chapter 1 describes the motivation for this work. Chapter 2 is an assessment of the seasonal cycle of pCO₂ on the Oregon shelf from both ship and mooring data. Results from this work demonstrate strong seasonality on the shelf, as well as interannual variability important for constraining regional flux estimates. The observations included the highest surface water pCO₂ reported for the region, and prolonged exposure of this water to the atmosphere had a large impact on the annual estimate of sea-air CO₂ flux. Chapter 3 presents a new data set of ship-based pCO₂ observations made over a larger portion of the western Canadian coastal margin than had been previously sampled during winter, summer and autumn. Analyses of temporally well-resolved historical data collected on the southwest Vancouver Island shelf, combined with the spatially well-resolved new data showed that CO₂ outgassing during autumn is significantly greater than during winter over most of the margin, and both seasons play a key role in nearly balancing the influx of atmospheric CO₂ that occurs during the remainder of the year. Chapter 4 reports water-air CO₂ fluxes from the Columbia River Estuary and plume across three seasons. The river plume is always a sink for atmospheric CO₂, likely from a combination of chemical and biological factors, while the estuary sink/source character is seasonally modified. During spring, the estuary acts as a sink for atmospheric CO₂, whereas it is a source during other seasons. Primary productivity and ecosystem respiration are important for determining the magnitude of fluxes in the estuary between seasons, and the spring freshet marks the transition between CO₂ sink and source functionality in the estuary. Chapter 5 examines the weak phytoplankton response to strong and persistent upwelling on the Oregon shelf in July 2008 to understand the prolonged exposure of high-pCO₂ water. Using ship, mooring and satellite data, I argue the phytoplankton response time is long relative to the timescales of strong upwelling, cross shore transport, and subduction. The rapid physical processes are most likely responsible for maintaining low chlorophyll conditions when nutrients and pCO₂ are elevated. Chapter 6 is a discussion of the importance of the large flux events observed during these studies, and their relevance to regional and global CO₂ flux studies. In each region studied in this thesis there were occurrences of high-intensity pCO₂ conditions, which highlights the variable nature of the coastal ocean and the importance of resolving the temporal and spatial scales of variability in order to assess continental margin sea-air CO2 fluxes

Results from the Baynes Sound Environmental Intelligence Collaboration (BaSEIC)

Baynes Sound, in the northern Salish Sea, hosts more than 50% of the BC shellfish aquaculture industry, with Pacific oyster (Magallana gigas) as the dominant production species. The known vulnerability of this species to ocean acidification (OA)-driven changes in seawater chemistry – specifically through alteration in calcium carbonate (CaCO3) mineral stability, combined with periodic production problems in Baynes Sound – have led to a growing concern regarding possible contemporaneous impacts of OA in spite of lacking environmental intelligence detailing baseline conditions. In order to build our understanding of current biogeochemical patterns in this key Salish Sea setting, the BC Shellfish Growers Association and the Hakai Institute, with support from partnering shellfish growers, the Province of British Columbia and the Tula Foundation, formed a research initiative, known as the Baynes Sound Environmental Intelligence Collaboration (BaSEIC), in early 2016. Seasonally-resolved and spatially-distributed discrete seawater samples were collected by shellfish growers and an independent citizen science group operating in the area. Discrete measurements were used to add spatial context to a high-frequency data stream produced by instrumentation installed at a shore-side facility for continuous observing of in situ (8 m) CO2 chemistry. Taken together, the discretely-collected and continuously-measured seawater CO2 data provide a dynamic picture of the baseline conditions in Baynes Sound, including: (1) a pronounced seasonal cycle with surface-focused favorable conditions for CaCO3 mineral precipitation between spring and early autumn, (2) a sharp decrease in mineral stability of sub-surface water including excursions toward CaCO3 undersaturated conditions during the winter season and summer neap tides, and (3) a seasonal north-south gradient in mineral stability. These results illustrate the current CO2 system patterns in Baynes Sound that are now being considered in shellfish industry management discussions

Impact of tropical instability waves on nutrient and chlorophyll distributions in the equatorial Pacific

Tropical instability waves (TIWs) are prominent seasonal features in both the equatorial Pacific and Atlantic Oceans. This work quantifies their role in modulating the distributions of nutrients and phytoplankton biomass. Using an eight year record of biannual ship observations along the Tropical Atmosphere Ocean (TAO) buoy array, cruise sections crossing TIWs were identified. Both a case study approach of individual TIWs and a first attempt at calculating their average effect on mixed layer properties were performed. Examination of individual TIWs demonstrates that their effect on nutrient and chlorophyll distributions is a function of the TIW intensity. Both strong and weak TIWs drive elevated nutrient concentrations directly on the equator, but strong TIWs possess enhanced recirculation which advects nutrient- and chlorophyll-poor waters from adjacent to the upwelling zone equatorward. This decreases nutrient concentrations from approximately 2°N to 8°N. Weak TIWs retain elevated nutrient concentrations in this latitudinal band due to less recirculation in TIW vortices, permitting chlorophyll increases. These differences between strong and weak TIWs were only observed north of the equator. Less recirculation was observed in TIW vortices south of the equator. This resulted in nutrient enhancements from TIWs along the southern portions of the cruise sections, especially in the eastern Pacific. The differences between northern and southern TIW dynamics suggest strong differences in TIW modulated carbon cycling between the two hemispheres. Seasonal modification of the equatorial currents also influences the extent to which TIWs alter nutrient and chlorophyll distributions. TIWs observed during boreal winter demonstrated enhanced nutrient and chlorophyll concentrations north of the equator. This resulted from the water mass north of the upwelling zone containing elevated nutrient and chlorophyll concentrations due to a shallow thermocline. Thermocline shoaling in boreal winter is the result of a slowing in the South Equatorial Current and North Equatorial Countercurrent caused by the seasonal decrease in westward trade wind velocities. These results suggest that there is a synergistic effect from TIWs and the seasonal shoaling of the thermocline which may be important for carbon cycling north of the equator. Composites of average mixed layer nutrient concentrations show TIW-induced nutrient enhancement on and south of the equator along most of the TAO lines, but no subsequent increase in mixed layer chlorophyll. This is likely due to the lag time between nutrient enhancement and biomass increase and/or chlorophyll increases in unsampled portions of the vortex. Regions of elevated chlorophyll concentrations were observed in SeaWiFS composites in unsampled portions of TIWs, which suggests that TIW induced lateral transport of nutrients may be driving important episodic export events south of the equator

Ocean acidification in the surface waters of the Pacific-Arctic boundary regions

Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 2 (2015): 122-135, doi:10.5670/oceanog.2015.36.The continental shelves of the Pacific-Arctic Region (PAR) are especially vulnerable to the effects of ocean acidification (OA) because the intrusion of anthropogenic CO2 is not the only process that can reduce pH and carbonate mineral saturation states for aragonite (Ωarag). Enhanced sea ice melt, respiration of organic matter, upwelling, and riverine inputs have been shown to exacerbate CO2 -driven ocean acidification in high-latitude regions. Additionally, the indirect effect of changing sea ice coverage is providing a positive feedback to OA as more open water will allow for greater uptake of atmospheric CO2 . Here, we compare model-based outputs from the Community Earth System Model with a subset of recent ship-based observations, and take an initial look at future model projections of surface water Ωarag in the Bering, Chukchi, and Beaufort Seas. We then use the model outputs to define benchmark years when biological impacts are likely to result from reduced Ωarag. Each of the three continental shelf seas in the PAR will become undersaturated with respect to aragonite at approximately 30-year intervals, indicating that aragonite undersaturations gradually progress upstream along the flow path of the waters as they move north from the Pacific Ocean. However, naturally high variability in Ωarag may indicate higher resilience of the Bering Sea ecosystem to these low-Ωarag conditions than the ecosystems of the Chukchi and the Beaufort Seas. Based on our initial results, we have determined that the annual mean for Ωarag will pass below the current range of natural variability in 2025 for the Beaufort Sea and 2027 for the Chukchi Sea. Because of the higher range of natural variability, the annual mean for Ωarag for the Bering Sea does not pass out of the natural variability range until 2044. As Ωarag in these shelf seas slips below the present-day range of large seasonal variability by mid-century, the diverse ecosystems that support some of the largest commercial and subsistence fisheries in the world may be under tremendous pressure.This project was funded by the National Science Foundation (PLR- 1041102 and AGS-1048827)

The story so far: an in situ pairing of chemical oceanography and physiology

Climate change is a pressing environmental concern, and understanding how abiotic variation contributes to population dynamics and persistence may ultimately predict the fates of species. Ocean acidification negatively impacts a range of species, including those using calcium carbonate for shell formation such as shellfish, which are important as ecosystem engineers and for food security. While much is known about carbonate chemistry and impacts of ocean acidification on the U.S. Pacific coast, there is limited regional information in British Columbia (BC), especially in socio-economically important coastal zones for aquaculture and migrating fisheries populations. Laboratory experimentation mimicking future climate scenarios provide valuable information on biological impacts under controlled conditions, but do not take into account the natural environmental fluctuations of coastal environments that may influence population persistence. This research program combines lower trophic level monitoring (plankton analysis), physiological responses (functional genomics of commercial bivalves) and high speed near real-time oceanographic monitoring at a field site in the northern Salish Sea, to provide information on system variability and its biological impacts on coastal ecosystems. Site abiotic variability will be discussed in the context of pre-industrial to current condition effects on species. Shellfish gene expression data will focus on population plasticity or microevolutionary adaptation to seasonal, optimal and sub-optimal calcium carbonate conditions over the short and long-term

Changes in the arctic ocean carbon cycle with diminishing ice cover

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in DeGrandpre, M., Evans, W., Timmermans, M., Krishfield, R., Williams, B., & Steele, M. Changes in the arctic ocean carbon cycle with diminishing ice cover. Geophysical Research Letters, 47(12), (2020): e2020GL088051, doi:10.1029/2020GL088051.Less than three decades ago only a small fraction of the Arctic Ocean (AO) was ice free and then only for short periods. The ice cover kept sea surface pCO2 at levels lower relative to other ocean basins that have been exposed year round to ever increasing atmospheric levels. In this study, we evaluate sea surface pCO2 measurements collected over a 6‐year period along a fixed cruise track in the Canada Basin. The measurements show that mean pCO2 levels are significantly higher during low ice years. The pCO2 increase is likely driven by ocean surface heating and uptake of atmospheric CO2 with large interannual variability in the contributions of these processes. These findings suggest that increased ice‐free periods will further increase sea surface pCO2, reducing the Canada Basin's current role as a net sink of atmospheric CO2.This research was made possible by grants from the NSF Arctic Observing Network program (ARC‐1107346, PLR‐1302884, PLR‐1504410, and OPP‐1723308). In addition, M. S. was supported by ONR (Grant 00014‐17‐1‐2545), NASA (Grant NNX16AK43G), and NSF (Grants PLR‐1503298 and OPP‐1751363)

Seasonal cycle of surface ocean pCO₂ on the Oregon shelf

Previous work has shown that the Oregon shelf is a sink for atmospheric carbon dioxide (CO₂) during the upwelling season; however, until now, summertime variability in CO₂ exchange and sign of the flux for the rest of the year were unknown. Observations of the partial pressure of CO₂ (pCO₂) in surface waters from August 2007 to May 2010 from ships and a buoy were used with historical data to produce a composite seasonal cycle for the central Oregon midshelf. These data indicate that the region is highly variable, at times being either a sink or strong source for atmospheric CO₂. Interannual wind variability was an important determining factor in shaping the sink/source nature of this system. Late summer and early autumn was most variable relative to the rest of the year. Winter pCO₂ was near or slightly below atmospheric levels. Strong shelf-wide undersaturated conditions were first observed in early spring and lasted until the upwelling season became developed. Peak upwelling season pCO₂ ranged from 1000 μatm. In July 2008, ship and buoy data revealed previously unobserved high-pCO₂ waters (∼1000 μatm) at the surface. These conditions persisted for nearly 2 months and drove this system to be only a weak net annual atmospheric CO₂ sink of −0.3 ± 6.8 mol m⁻² yr⁻¹. These data showed, for the first time, the seasonal cycle of surface ocean pCO₂ on the central Oregon midshelf and the impact of heretofore undocumented pCO₂ levels on an estimate of sea-air CO₂ flux for this region.This is the publisher's final pdf. The published article is copyrighted by American Geophysical Union and can be found at: http://www.agu.org/journals/jc

Annual sea-air CO2fluxes in the Bering Sea: insights from new autumn and winter observations of a seasonally ice-covered continental shelf

High-resolution data collected from several programs have greatly increased the spatiotemporal resolution of pCO2(sw) data in the Bering Sea, and provided the first autumn and winter observations. Using data from 2008 to 2012, monthly climatologies of sea-air CO2 fluxes for the Bering Sea shelf area from April to December were calculated, and contributions of physical and biological processes to observed monthly sea-air pCO2 gradients (?pCO2) were investigated. Net efflux of CO2 was observed during November, December, and April, despite the impact of sea surface cooling on ?pCO2. Although the Bering Sea was believed to be a moderate to strong atmospheric CO2 sink, we found that autumn and winter CO2 effluxes balanced 65% of spring and summer CO2 uptake. Ice cover reduced sea-air CO2 fluxes in December, April, and May. Our estimate for ice-cover corrected fluxes suggests the mechanical inhibition of CO2 flux by sea-ice cover has only a small impact on the annual scale (<2%). An important data gap still exists for January to March, the period of peak ice cover and the highest expected retardation of the fluxes. By interpolating between December and April using assumptions of the described autumn and winter conditions, we estimate the Bering Sea shelf area is an annual CO2 sink of ?6.8 Tg C yr?1. With changing climate, we expect warming sea surface temperatures, reduced ice cover, and greater wind speeds with enhanced gas exchange to decrease the size of this CO2 sink by augmenting conditions favorable for greater wintertime outgassing

Creativity and cognitive skills among millenials: thinking too much and creating too little

Organizations crucially need the creative talent of millennials but are reluctant to hire them because of their supposed lack of diligence. Recent studies have shown that hiring diligent millennials requires selecting those who score high on the Cognitive Reflection Test (CRT) and thus rely on effortful thinking rather than intuition. A central question is to assess whether the push for recruiting diligent millennials using criteria such as cognitive reflection can ultimately hamper the recruitment of creative workers. To answer this question, we study the relationship between millennials’ creativity and their performance on fluid intelligence (Raven) and cognitive reflection (CRT) tests. The good news for recruiters is that we report, in line with previous research, evidence of a positive relationship of fluid intelligence, and to a lesser extent cognitive reflection, with convergent creative thinking. In addition, we observe a positive effect of fluid intelligence on originality and elaboration measures of divergent creative thinking. The bad news for recruiters is the inverted U-shape relationship between cognitive reflection and fluency and flexibility measures of divergent creative thinking. This suggests that thinking too much may hinder important dimensions of creative thinking. Diligent and creative workers may thus be a rare find

Diverse modes of binding in structures of Leishmania major N-myristoyltransferase with selective inhibitors

The leishmaniases are a spectrum of global diseases of poverty associated with immune dysfunction and are the cause of high morbidity. Despite the long history of these diseases, no effective vaccine is available and the currently used drugs are variously compromised by moderate efficacy, complex side effects and the emergence of resistance. It is therefore widely accepted that new therapies are needed. N-Myristoyltransferase (NMT) has been validated pre-clinically as a target for the treatment of fungal and parasitic infections. In a previously reported high-throughput screening program, a number of hit compounds with activity against NMT from Leishmania donovani have been identified. Here, high-resolution crystal structures of representative compounds from four hit series in ternary complexes with myristoyl-CoA and NMT from the closely related L. major are reported. The structures reveal that the inhibitors associate with the peptide-binding groove at a site adjacent to the bound myristoyl-CoA and the catalytic -carboxylate of Leu421. Each inhibitor makes extensive apolar contacts as well as a small number of polar contacts with the protein. Remarkably, the compounds exploit different features of the peptide-binding groove and collectively occupy a substantial volume of this pocket, suggesting that there is potential for the design of chimaeric inhibitors with significantly enhanced binding. Despite the high conservation of the active sites of the parasite and human NMTs, the inhibitors act selectively over the host enzyme. The role of conformational flexibility in the side chain of Tyr217 in conferring selectivity is discussed