Ocean In Spring Research Articles

Aerosol effects on liquid cloud microphysical properties in south China: Land–ocean contrasts

The aerosol effects on liquid cloud microphysical properties over South China and adjacent ocean regions are investigated by using aerosol reanalysis data from MERRA-2, cloud property data from CLARA-A2, and reanalysis data from ERA5 from 1995 to 2015. The aerosol optical depth (AOD) in South China and adjacent ocean regions shows an upward trend with obvious land–ocean contrasts. The AOD is significantly positively correlated with the liquid cloud droplet effective radius (LREF) over both land and the ocean in summer and autumn, while increasing AOD significantly suppresses the LREF in spring and winter over land. This indicates that the thermal supply is likely the reason for the differences in aerosol effects on liquid cloud properties in different seasons. The weak correlation between the AOD and LREF over the ocean in spring may be because the South China Sea monsoon onset increases the atmospheric instability, and springtime in southeastern China is characterized by high rainfall. This indicates that the effects of aerosols on clouds are not as significant as those on large-scale systems. Further analysis shows that the aerosol effects on the liquid cloud properties are strong and positive at low liquid water paths (LWP) in summer and autumn, while the effect is weak at high LWPs. This may be due to the presence of sufficient liquid water droplets with large LWPs in summer and autumn, and few liquid water droplets in spring and winter. The aerosol effects on liquid cloud properties also significantly depend on lower-tropospheric stability (LTS).

Nanoplankton: The dominant vector for carbon export across the Atlantic Southern Ocean in spring.

Across the Southern Ocean, large (≥20 μm) diatoms are generally assumed to be the primary vector for carbon export, although this assumption derives mainly from summertime observations. Here, we investigated carbon production and export potential during the Atlantic Southern Ocean's spring bloom from size-fractionated measurements of net primary production (NPP), nitrogen (nitrate, ammonium, urea) and iron (labile inorganic iron, organically complexed iron) uptake, and a high-resolution characterization of phytoplankton community composition. The nanoplankton-sized (2.7 to 20 μm) diatom, Chaetoceros spp., dominated the biomass, NPP, and nitrate uptake across the basin (40°S to 56°S), which we attribute to their low iron requirement, rapid response to increased light, and ability to escape grazing when aggregated into chains. We estimate that the spring Chaetoceros bloom accounted for >25% of annual export production across the Atlantic Southern Ocean, a finding consistent with recent observations from other regions highlighting the central role of the phytoplankton "middle class" in carbon export.

Microphysical and thermodynamic phase analyses of Arctic low-level clouds measured above the sea ice and the open ocean in spring and summer

Abstract. Airborne in situ cloud measurements were carried out over the northern Fram Strait between Greenland and Svalbard in spring 2019 and summer 2020. In total, 811 min of low-level cloud observations were performed during 20 research flights above the sea ice and the open Arctic ocean with the Polar 5 research aircraft of the Alfred Wegener Institute. Here, we combine the comprehensive in situ cloud data to investigate the distributions of particle number concentration N, effective diameter Deff, and cloud water content CWC (liquid and ice) of Arctic clouds below 500 m altitude, measured at latitudes between 76 and 83∘ N. We developed a method to quantitatively derive the occurrence probability of their thermodynamic phase from the combination of microphysical cloud probe and Polar Nephelometer data. Finally, we assess changes in cloud microphysics and cloud phase related to ambient meteorological conditions in spring and summer and address effects of the sea ice and open-ocean surface conditions. We find median N from 0.2 to 51.7 cm−3 and about 2 orders of magnitude higher N for mainly liquid clouds in summer compared to ice and mixed-phase clouds measured in spring. A southerly flow from the sea ice in cold air outbreaks dominates cloud formation processes at temperatures mostly below −10 ∘C in spring, while northerly warm air intrusions favor the formation of liquid clouds at warmer temperatures in summer. Our results show slightly higher N in clouds over the sea ice compared to the open ocean, indicating enhanced cloud formation processes over the sea ice. The median CWC is higher in summer (0.16 g m−3) than in spring (0.06 g m−3), as this is dominated by the available atmospheric water content and the temperatures at cloud formation level. We find large differences in the particle sizes in spring and summer and an impact of the surface conditions, which modifies the heat and moisture fluxes in the boundary layer. By combining microphysical cloud data with thermodynamic phase information from the Polar Nephelometer, we find mixed-phase clouds to be the dominant thermodynamic cloud phase in spring, with a frequency of occurrence of 61 % over the sea ice and 66 % over the ocean. Pure ice clouds exist almost exclusively over the open ocean in spring, and in summer the cloud particles are most likely in the liquid water state. The comprehensive low-level cloud data set will help us to better understand the role of clouds and their thermodynamic phase in the Arctic radiation budget and to assess the performance of global climate models in a region of the world with the strongest anthropogenic climate change.

Paleoclimate of Titan with hydrocarbon oceans and continents simulated by a global climate model

Titan’s paleoclimate in the presence of hypothetical hydrocarbon oceans 1 Gyr ago is simulated by a global climate model with a slab ocean model. Simulations are run for two different ocean compositions and with and without continents. The climate over ethane-rich oceans is dry with respect to methane but is windier than over methane-rich oceans. Continents do not substantially change the climate if the ocean is ethane-rich but continents are somewhat windier than the oceans for orographic reasons. The climate over methane-rich oceans is very moist but calm as long as there are no continents. Global imbalance between the N2 release from the ocean in spring and N2 absorption by the ocean in autumn due to the temperature dependence of the N2 solubility in the ocean causes a semi-annual variation in global-mean surface pressure by ∼0.1 hPa. Continents surrounded by methane-rich oceans induce a sea breeze circulation in summer due to a sea-land temperature contrast. The sea breeze causes intense orographic precipitation on windward slopes of continents. Possible presence of circum-Xanadu continents surrounded by methane-rich oceans may have been conducive to the formation of the observed numerous fluvial networks in Xanadu.

Seasonal variation of fluxes of planktic foraminiferal tests collected by a time-series sediment trap in the central Bay of Bengal during three different years

Sediment trap samples from the southwestern Bay of Bengal were obtained at a water depth of about 900 m at sampling intervals of 17–27 days during three time periods (November 1988 to October 1989, December 1990 to October 1991, and January 1993 to October 1993). The planktic foraminifer abundances and assemblages of the samples were analyzed, and the factors governing the assemblages and their potential as indicators of climate and ocean processes in the sedimentary record were examined. We identified 28 species of planktic foraminifers in the samples, of which seven species accounted for more than 80% of each assemblage. The highest fluxes of planktic foraminifer tests were generally observed during the summer and winter monsoon seasons, and the lowest fluxes were observed during the intermonsoon seasons, especially from March to May. Periods of enhanced primary production during monsoons were accompanied by a sharp increase in the flux of Globigerina bulloides, whereas nutrient depletion in the surface ocean in spring led to subsurface small size plankton production and low planktic foraminifer test fluxes. The seasonality of foraminiferal assemblages and fluxes was controlled mainly by seasonal surface and subsurface primary production. The transition of abundant species from subsurface dwellers to surface ones throughout the monsoon season can be attributed to initial subsurface primary and secondary production being succeeded by enhanced surface production. The foraminiferal flux pattern differed among the three observation periods, especially in summer, because of interannual variation in the regional physical forces that induce nutrient replenishment at the surface. However, the consistent features of the flux pattern, with peaks during the monsoon seasons and minimal values in spring, suggest that our results reveal the essential, long-term flux pattern of planktic foraminifers in the southwestern Bay of Bengal.

Responses of Arctic cyclones to biogeophysical feedbacks under future warming scenarios in a regional Earth system model

Arctic cyclones, as a prevalent feature in the coupled dynamics of the Arctic climate system, have large impacts on the atmospheric transport of heat and moisture and deformation and drifting of sea ice. Previous studies based on historical and future simulations with climate models suggest that Arctic cyclogenesis is affected by the Arctic amplification of global warming, for instance, a growing land-sea thermal contrast. We thus hypothesize that biogeophysical feedbacks (BF) over the land, here mainly referring to the albedo-induced warming in spring and evaporative cooling in summer, may have the potential to significantly change cyclone activity in the Arctic. Based on a regional Earth system model (RCA-GUESS) which couples a dynamic vegetation model and a regional atmospheric model and an algorithm of cyclone detection and tracking, this study assesses for the first time the impacts of BF on the characteristics of Arctic cyclones under three IPCC Representative Concentration Pathways scenarios (i.e. RCP2.6, RCP4.5 and RCP8.5). Our analysis focuses on the spring- and summer time periods, since previous studies showed BF are the most pronounced in these seasons. We find that BF induced by changes in surface heat fluxes lead to changes in land-sea thermal contrast and atmospheric stability. This, in turn, noticeably changes the atmospheric baroclinicity and, thus, leads to a change of cyclone activity in the Arctic, in particular to the increase of cyclone frequency over the Arctic Ocean in spring. This study highlights the importance of accounting for BF in the prediction of Arctic cyclones and the role of circulation in the Arctic regional Earth system.

In situ continuous observation of hourly elements in PM2.5 in urban beijing, China: Occurrence levels, temporal variation, potential source regions and health risks

Elements in fine particles (PM2.5) have adverse impacts on ecosystems and human health. Using an online multi-heavy metal analyzer, one-year continuous hourly measurements were performed for thirteen elements, namely, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Ba, Hg and Pb, from June 1, 2016, to May 31, 2017, in urban Beijing. The total concentrations of 13 elements were in the range of 114–136,574 ng/m3, with a mean concentration of 2534 ± 5563 ng/m3. The four dominated elements were K (900 ± 3554 ng/m3), Fe (738 ± 1485 ng/m3), Ca (493 ± 1473 ng/m3) and Zn (174 ± 189 ng/m3). The annual mean concentrations of Cr and As exceeded the guideline values of the World Health Organization and the Chinese National Ambient Air Quality Standard. In the absence of firework-burning episodes and heavy dust storms, K, Cr, Mn, Cu, Zn, As, Se, Hg and Pb showed higher concentrations in autumn and winter, whereas lower concentrations were observed in spring and summer. The higher concentrations of Ca, Fe, and Ba observed in spring were associated with the frequent occurrence of dust. All elements showed higher concentrations on weekends than on weekdays. The diel patterns of Fe, Ba, Ca, Cu, Zn, Ni and Mn showed higher concentrations during peak traffic periods, whereas those of As, Cr, Hg, K, Pb and Se showed lower concentrations in the daytime but higher ones in the nighttime. The potential source function (PSCF) identified that neighboring provinces were the major source regions for most elements, whereas Ni mainly came from Shandong and the eastern ocean in spring and summer. Health risks of PM2.5 elements (Cr, Mn, Ni, As, Ba and Pb) via the inhalation pathway were estimated. Mn (As) and As posed the highest noncarcinogenic and carcinogenic risks to human health, respectively. Overall, this work can provide more detailed information on the characteristics of elements for the science community and be used in other receptor modelling and health risk assessment studies.

Characteristics of Atmospheric PM2.5 Pollution and Its Influence on Visibility in Background Areas of Ji'nan

In order to study the seasonal variations in the chemical composition of atmospheric particulate matter with diameters less than 2.5 μm (PM2.5) and its influence on visibility in background areas, atmospheric PM2.5 samples were collected in spring, summer, autumn, and winter 2016 at Qixingtai in Ji'nan. The pollution characteristics of water-soluble ions components, organic carbon (OC), and elemental carbon (EC) were analyzed, and their regional transmission contributions were studied. The results show that NH4+, SO42-, and NO3- were the main components of water-soluble ions, accounting for 90.24% of the annual total ion concentration. The secondary water soluble inorganic ions were polluted severely. NO3-/SO42- presented obvious seasonal variations of high (low) levels in winter (summer). In each season, SO42- and NH4+ existed mainly in the form of (NH4)2SO4. The value of secondary OC (SOC)/OC ranged from 21.17% to 54.21%, indicating the presence of relatively severe secondary organic pollution in this area. The sulfur oxidation ratio (SOR) value in all seasons was greater than 0.1, indicating that the secondary generation of SO42- occurs in all seasons in this region, and the value of nitrogen oxidation ratio (NOR) in all seasons was higher than the SOR value. The secondary transformation of NO2 in the Qixingtai region was stronger than that of SO2. The range of atmospheric extinction coefficient (Bext) was 172.68-320.61 Mm-1, with an annual mean of 256.48 Mm-1. The atmospheric extinction coefficient showed an obvious seasonal trend of the lowest (highest) in summer (winter). The backward airflow trajectory shows that the Qixingtai was affected mainly by the long-distance transmission from Northwest China and the ocean in spring and summer and by local sources in autumn and winter. A comparison of the characteristics of atmospheric PM2.5 pollution in Ji'nan in 2008 revealed that the influence of motor vehicles on the atmospheric environment has been significantly improved.

Seasonal variation in migration strategies used to cross ecological barriers in a nearctic migrant wintering in Africa

Ecological barriers such as oceans, mountain ranges or glaciers can have a substantial influence on the evolution of animal migration. Along the migration flyway connecting breeding sites in the North American Arctic and wintering grounds in Europe or Africa, nearctic species are confronted with significant barriers such as the Atlantic Ocean and the Greenland icecap. Using geolocation devices, we identified wintering areas used by ringed plovers nesting in the Canadian High‐Arctic and investigated migration strategies used by these nearctic migrants along the transatlantic route. The main wintering area of the ringed plovers (n = 20) was located in western Africa. We found contrasting seasonal migration patterns, with ringed plovers minimizing continuous flight distances over the ocean in spring by making a detour to stop in Iceland. In autumn, however, most individuals crossed the ocean in one direct flight from southern Greenland to western Europe, as far as southern Spain. This likely resulted from prevailing anti‐clockwise winds associated with the Icelandic low‐pressure system. Moreover, the plovers we tracked largely circumvented the Greenland icecap in autumn, but in spring, some plovers apparently crossed the icecap above the 65°N. Our study highlighted the importance of Iceland as a stepping‐stone during the spring migration and showed that small nearctic migrants can perform non‐stop transatlantic flights from Greenland to southern Europe.

Characterization of Bacterial Communities in Bioaerosols over Northern Chinese Marginal Seas and the Northwestern Pacific Ocean in Spring

AbstractStudies of the community structures of bacteria in marine aerosols of different particle sizes have not been reported. Aerosol samples were collected using a six-stage bioaerosol sampler over the Bohai Sea, the Yellow Sea, and northwestern Pacific Ocean in the spring of 2014. The diversity and composition of these samples were investigated by Illumina high-throughput sequencing, and 130 genera were detected in all of the samples; the most abundant bacterial genus was Bacteroides, followed by Prevotella and Megamonas. The Chao1 and Shannon diversity indices ranged from 193 to 1044 and from 5.44 to 8.33, respectively. The bacterial community structure in coarse particles (diameter larger than 2.1 μm) was more complex and diverse than that in fine particles (diameter less than 2.1 μm) in marine bioaerosols from over the Yellow Sea and northwestern Pacific Ocean, while the opposite trend was observed for samples collected over the Bohai Sea. Although we were sampling over marine regions, the sources of the bioaerosols were mostly continental. Temperature and wind speed significantly influenced the bacterial communities in marine aerosols of different particle sizes. There may be a bacterial background in the atmosphere in the form of several dominant taxa, and the bacterial communities are likely mixed constantly during transmission.

Modern pollen distribution in the northeastern Indian Ocean and its significance.

In order to provide a reference for reconstructing the paleoclimate of the northeastern Indian Ocean, 36 airborne pollen samples were analyzed using methods for airborne pollen, and 26 surface water samples were analyzed using a lab method for surface water. We found that little pollen is airborne over the Indian Ocean in spring, but airborne pollen types and concentrations can help to deduce paleomonsoon strength and direction. The conclusions included the following: (1) Pollen in the sediment was transported mainly via ocean currents instead of the early summer or spring wind. (2) Airborne pollen types and concentrations are proportional to the wind speed and inversely proportional to the pollen distance transported and depend on whether the wind is from the land or from the sea. If the wind is from the land, the pollen concentration is proportional to the angle between the wind direction and the coastline. (3) The pollen concentration in the sample collected from a water depth of 30-45m is higher than in the samples collected from a depth of 5m. The pollen concentration and salinity are higher in the equatorial area than in the Northern Hemisphere.

Does Pacific Variability Influence the Northwest Atlantic Shelf Temperature?

AbstractThe relationship between North Pacific variability and sea surface temperature (SST) of the Northwest Atlantic continental shelf is examined over interannual time scale in 1982–2014. Statistically significant negative correlations exist between Pacific Decadal Oscillation (PDO) index and SST in the Gulf of Maine (GoM) in spring and summer. Cross‐correlation analysis further suggests significant negative lead‐lag correlations, with the spring PDO leading the GoM SST by 0–3 months while the summer PDO lags by 1–3 months. These correlations are dominated by the interannual component of the PDO. Statistical relationships are placed in context by further investigating the physical processes controlling the upper ocean mixed layer temperature budget in the GoM. The results reveal contrasting roles between the atmosphere and the ocean in spring and summer, respectively. Local atmospheric forcings, in particular the radiative air‐sea fluxes, are the dominant driver for the interannual variability of springtime SST over the Northwest Atlantic shelf. In contrast, oceanic terms are important in controlling the interannual variability of summertime SST. As a result, reconstructed SST using atmospheric forcings successfully reproduces the statistical relationship with PDO in spring, but not in summer. Furthermore, it is shown that the SST anomalies in the central and eastern North Pacific play a key role in these relationships.

Availability of holding habitat in lakes and rivers affects the incidence of spring (premature) upriver migration by Atlantic salmon

Premature migration is a key component of the biocomplexity of anadromous fishes, yet remains poorly understood. Many Atlantic salmon (Salmo salar) populations leave the ocean in spring, months prior to spawning, though this curtails feeding in productive marine environments. We hypothesized that habitat features encourage the evolution of this trait by providing fish with physical and thermal refuge during their long freshwater holding period. We document substantial variation in Atlantic salmon return-migration timing across 70 Irish rivers using 8 years of angling data, validated with electronic-counter data from 23 of the rivers. A higher frequency of spring migrating salmon was observed in rivers with accessible lakes and larger rivers in general. Spring migration may have evolved in rivers with suitable holding habitat as a strategy to minimize cumulative marine mortality, which is traded off against additional marine feeding. More research on this neglected topic is needed, given the value of large spring migrating Atlantic salmon to anglers, ongoing declines in their abundance in Ireland and elsewhere, and the widespread occurrence of premature migration in salmonids generally.

Subthermocline eddies observed by rapid‐sampling Argo floats in the subtropical northwestern Pacific Ocean in Spring 2014

AbstractIn Spring 2014, two subthermocline eddies (STEs) were observed by rapid‐sampling Argo floats in the subtropical northwestern Pacific (STNWP). The first one is a warm, salty, and oxygen‐poor lens, with its temperature/salinity /dissolved oxygen (T/S/DO) anomalies reaching 1.16°C/0.21 practical salinity unit (psu)/−29.9 µmol/kg, respectively, near the 26.62σ0 surface. The other is a cold, fresh, and oxygen‐rich lens, with its T/S/DO anomalies reaching −1.95°C/−0.34 psu/88.0 µmol/kg, respectively, near the 26.54σ0 surface. The vertical extent of the water mass anomalies in the warm (cold) STE is about 190 m (150 m), and its horizontal length scale is 22 ± 7 km (18 ± 10 km). According to their water mass properties, we speculate that the warm and cold STEs are generated in the North Pacific Subtropical and Subarctic Front region, respectively. The observed STEs may play an important role in modifying the intermediate‐layer water properties in the STNWP, and this needs to be confirmed by more focused observations in the future.

Impact of sea ice on the marine iron cycle and phytoplankton productivity

Abstract. Iron is a key nutrient for phytoplankton growth in the surface ocean. At high latitudes, the iron cycle is closely related to the dynamics of sea ice. In recent decades, Arctic sea ice cover has been declining rapidly and Antarctic sea ice has exhibited large regional trends. A significant reduction of sea ice in both hemispheres is projected in future climate scenarios. In order to adequately study the effect of sea ice on the polar iron cycle, sea ice bearing iron was incorporated in the Community Earth System Model (CESM). Sea ice acts as a reservoir for iron during winter and releases the trace metal to the surface ocean in spring and summer. Simulated iron concentrations in sea ice generally agree with observations in regions where iron concentrations are relatively low. The maximum iron concentrations simulated in Arctic and Antarctic sea ice are much lower than observed, which is likely due to underestimation of iron inputs to sea ice or missing mechanisms. The largest iron source to sea ice is suspended sediments, contributing fluxes of iron of 2.2 × 108 mol Fe month−1 in the Arctic and 4.1 × 106 mol Fe month−1 in the Southern Ocean during summer. As a result of the iron flux from ice, iron concentrations increase significantly in the Arctic. Iron released from melting ice increases phytoplankton production in spring and summer and shifts phytoplankton community composition in the Southern Ocean. Results for the period of 1998 to 2007 indicate that a reduction of sea ice in the Southern Ocean will have a negative influence on phytoplankton production. Iron transport by sea ice appears to be an important process bringing iron to the central Arctic. The impact of ice to ocean iron fluxes on marine ecosystems is negligible in the current Arctic Ocean, as iron is not typically the growth-limiting nutrient. However, it may become a more important factor in the future, particularly in the central Arctic, as iron concentrations will decrease with declining sea ice cover and transport.

Low-level jet characteristics over the Arctic Ocean in spring and summer

Abstract. Low-level jets (LLJ) are important for turbulence in the stably stratified atmospheric boundary layer, but their occurrence, properties, and generation mechanisms in the Arctic are not well known. We analysed LLJs over the central Arctic Ocean in spring and summer 2007 on the basis of data collected in the drifting ice station Tara. Instead of traditional radiosonde soundings, data from tethersonde soundings with a high vertical resolution were used. The Tara results showed a lower occurrence of LLJs (46 ± 8%) than many previous studies over polar sea ice. Strong jet core winds contributed to growth of the turbulent layer. Complex relationships between the jet core height and the temperature inversion top height were detected: substantial correlation (r = 0.72; p < 0.01) occurred when the jet core was above the turbulent layer, but when inside the turbulent layer there was no correlation. The most important forcing mechanism for LLJs was baroclinicity, which was responsible for the generation of strong and warm LLJs, which on average occurred at lower altitudes than other jets. Baroclinic jets were mostly associated with transient cyclones instead of the climatological air temperature gradients. Besides baroclinicity, cases related to inertial oscillations and gusts were detected. As many as 49% of the LLJs observed were associated with a frontal passage, which provides favourable conditions for baroclinicity, inertial oscillations, and gusts. Further research needs on LLJs in the Arctic include investigation of low-level jet streams and their effects on the sea ice drift and atmospheric moisture transport.

Dominant climate factors influencing the Arctic runoff and association between the Arctic runoff and sea ice

By using the Arctic runoff data from R-ArcticNET V4.0 and ArcticRIMS, trends of four major rivers flowing into the Arctic Ocean, whose climate factor plays an important role in determining the variability of the Arctic runoff, are investigated. The results show that for the past 30 years, the trend of the Arctic runoff is seasonally dependent. There is a significant trend in spring and winter and a significant decreasing trend in summer, leading to the reduced seasonal cycle. In spring, surface air temperature is the dominant factor influencing the four rivers. In summer, precipitation is the most important factor for Lena and Mackenzie, while snow cover is the most important factor for Yenisei and Ob. For Mackenzie, atmospheric circulation does play an important role for all the seasons, which is not the case for the Eurasian rivers. The authors further discuss the relationships between the Arctic runoff and sea ice. Significant negative correlation is found at the mouth of the rivers into the Arctic Ocean in spring, while significant positive correlation is observed just at the north of the mouths of the rivers into the Arctic in summer. In addition, each river has different relationship with sea ice in the eastern Greenland Sea.

Relationships among upwelling, phytoplankton blooms, and phycotoxins in coastal Oregon shellfish

Climatologies derived from satellite data (1998 to 2007) were used to elucidate seasonal and latitudinal patterns in winds, sea surface temperature (SST), and chlorophyll concentrations (chl) over the Oregon shelf. These were further used to reveal oceanographic conditions normally associ- ated with harmful algal blooms (HABs) and toxic shellfish events along the Oregon coast. South of 43° N, around Cape Blanco, summer upwelling started earlier and finished later than north of 43° N. Spring blooms occur when light limitation is relieved, before the initiation of upwelling, and sec- ondary, more intense blooms occur approximately 2 wk after upwelling is established. North of 45° N, SST and chl are heavily influenced by the Columbia River plume, which delays upwelling-driven cooling of the surface coastal ocean in spring, and causes phytoplankton blooms (as indicated by increased chl) earlier than expected. The presence of saxitoxin in coastal shellfish, which causes paralytic shellfish poisoning, was generally associated with late summer upwelling. The presence of domoic acid in shellfish, which leads to amnesic shellfish poisoning, was greatest during the transi- tion between upwelling and downwelling regimes. This work demonstrates that satellite data can indicate physical situations when HABs are more likely to occur, thus providing a management tool useful in predicting or monitoring HABs.

Elevated biogenic sulphur dioxide concentrations over the North Atlantic

Elevated biogenic SO 2 from the oxidation of dimethylsulphide (DMS) in the marine atmosphere was measured over the North Atlantic Ocean in spring and summer 2003. Stable isotope apportionment was used to distinguish between anthropogenic and biogenic SO 2 in the marine atmosphere south of Greenland. Atmospheric DMS measurements were within range of previous studies. Biogenic SO 2 concentrations were as high as 82 nmol m −3 (spring geometric mean: 4 nmol m −3, σ = 17; summer geometric mean 7 nmol m −3, σ = 19) and are the highest reported values for marine biogenic SO 2 in the literature. Elevated biogenic SO 2 was found in air masses influenced by anthropogenic pollutants during the summer. This indicates that anthropogenic pollutants may affect the fate of oceanic emissions of sulphur compounds in the atmosphere favoring the formation of cloud condensation nuclei.

Synoptic influences on springtime tropospheric O<sub>3</sub> and CO over the North American export region observed by TES

Abstract. The relationship between synoptic circulation patterns over the western North Atlantic Ocean in spring (March, April, and May) and tropospheric O3 and CO was investigated using retrievals from the Tropospheric Emission Spectrometer (TES) for 2005 and 2006. Seasonal composites of TES retrievals reprocessed to remove the artificial geographic structure added from the a priori revealed a channel of slightly elevated O3 (>55 ppbv) and CO (>115 ppbv) at the 681 hPa retrieval level between 30° N and 45° N extending from North America out over the Atlantic Ocean. Ozone and CO in this region were correlated at r=0.22 with a slope value of 0.13 mol mol−1 indicative of the overall impact of photochemical chemical processes in North American continental export. Composites of TES retrievals for the six predominant circulation patterns identified as map types from sea level pressure fields of the NCEP FNL analyses showed large variability in the distribution of tropospheric O3. Map types MAM2 and MAM3 featuring cyclones near the US east coast produced the greatest export to the lower free troposphere with O3>65 ppbv and a relatively well-defined O3-CO correlation (slope values near 0.20 mol mol−1). The ensembles of HYSPLIT backward trajectories indicated that the high O3 levels were possibly a result of pollutants lofted to the free troposphere by the warm conveyor belt (WCB) of a cyclone. An important finding was that pollutant export occurred in the main WCB branch to the east of the cyclone and in a secondary branch circling to the back of the cyclone center. Conversely, a map type featuring a large anticyclone dominating the flow over the US east coast (MAM6) restricted export with O3 levels generally <55 ppbv and CO levels generally <110 ppbv. There was also evidence of stratospheric intrusions particularly to the north of 45° N in the 316 hPa composites predominately for MAM1 which featured a large cyclone near Newfoundland. However, the concurrence of these intrusions with pollutant export, specifically in the southwestern North Atlantic Ocean, made it difficult to delineate their respective contributions to the 681 hPa O3 composites.