Atlantic Coastal Site Research Articles

Short-term trend and temporal variations in atmospheric methane at an Atlantic coastal site in Southwestern Europe

Methane (CH4) was measured at El Arenosillo observatory, in an Atlantic coastal area located in Southwestern Europe, throughout a four-year period (September 2019–December 2023). Short-term trend, temporal variations and patterns were explored. A trend of 12.1 ± 1.1 nmol mol−1 year−1 was obtained based on daily averages. CH4 exhibited its highest mole fraction in cold months and its lowest in summer, and a seasonally varying diurnal cycle was also observed, with peaks in the early morning (7:00–8:00 UTC) and minimum values at 18:00–19:00 UTC. Mitigation strategies should be implemented based on an understanding of CH4 patterns. To achieve this, CH4 variations under an atmosphere governed by two synoptic patterns were studied. The atmospheric dynamic was analysed with the wind fields from ERA5 data reanalysis and the air masses pathways with the back-trajectories computed with the HYSPLIT model. CH4 horizontal distribution was explored with the TROPOMI observations. The CH4 baseline was collected under the influence of Atlantic air, while a rise from 40 to 80 nmol mol−1 was found with continental airflows from the inland Guadalquivir Valley. CH4 under sea-land breezes did not contribute to the increase of CH4. However, XCH4 from TROPOMI showed an accumulation in the marine area of the Gulf of Cadiz. Ongoing CH4 observations will be used to identify potential changes in the trend, understand the contribution of transported CH4 from areas such as the Western Mediterranean Basin, or assess its impact on surface ozone, among other objectives.

Invasive green crab, Carcinus maenas, on the Atlantic coast and in the Bras d'Or Lakes of Nova Scotia, Canada: larval supply and recruitment

Patterns in larval supply and recruitment of the invasive European green crab, Carcinus maenas, were examined at two sites in Nova Scotia, Canada: a typical Atlantic coastal site with high salinity (∼33) and strong tidal signal (Terence Bay); and a microtidal site in the Bras d'Or Lakes, where surface salinity fluctuated from 0 to 23 (Benacadie Pond). Abundance of all life history stages (zoeae, megalopae, juveniles and ovigerous females) was sampled approximately biweekly at each site from June 2001 to June 2002. The reproductive season, based on the presence of ovigerous females, is ∼5 months (June to October) at both sites. Zoeae-I were collected from June to July 2001 and in June 2002 at Terence Bay, and from June to August 2001 at Benacadie Pond. We did not collect later zoeal stages at either site. Megalopae were collected from September to October 2001 at Terence Bay, and from August to September 2001 at Benacadie Pond. Juveniles 1–6 mm carapace width (CW) were present throughout the summer at Terence Bay, and only in autumn at Benacadie. Juveniles 6–12 and 12–27 mm CW were present throughout the summer and autumn at both sites. At Terence Bay, densities of 1–6 and 12–27 mm CW juveniles did not vary among intertidal zones. In contrast, the 6–12 mm CW size-class appeared to move higher in the intertidal through the season, possibly due to effects of predation.

Photostationary state deviation–estimated peroxy radicals and their implications for HOx and ozone photochemistry at a remote northern Atlantic coastal site

Measurements of NO, NO2, O3, and ultraviolet irradiance made at Cape Norman, Newfoundland (51.6°N, 55.9°W), during February–April 1996 were used to examine peroxy radical photochemistry and the local photochemical ozone tendency. Deviations from NO‐NO2‐O3 photostationary state (the PSSD method) were used to estimate peroxy radical (PO2) mixing ratios. Potential biases in the PSSD method and the methods used to apply it in an unbiased manner are discussed. PO2 levels reached 77 ± 8 pptv (midday mean ±2σ of the mean), significantly higher than observed in previous studies at remote marine locations. [PO2] was well correlated with ()1/2, indicating that the dominant radical source was photolysis by ultraviolet radiation in the wavelength region of O3 photolysis and the dominant sink of PO2 was recombination. However, the variation of [PO2] with ()1/2 (d[PO2]/d()1/2) was significantly higher than expected at this site during spring. Significant radical production in addition to that from net O3 photolysis, possibly related to snow photochemistry in the upwind region, is suggested as the cause. However, the measurements needed to test this hypothesis were not made in this study, and we suggest future HOx measurements in remote midlatitude, snow‐covered regions. The net photochemical ozone production at this site during springtime was calculated to be minimal (generally small and negative, and always less than or equal to +0.1 ppbv/h). These small values indicate that in situ photochemical ozone production is negligible at this site during spring; if [HO2]/[PO2] is large, net ozone destruction may contribute up to ∼10% of mean ozone levels per day.

Multiproxy Devensian Late‐glacial and Holocene environmental records at an Atlantic coastal site in Shetland

AbstractMarine erosion at Clettnadal, West Burra island off the west coast of Shetland, caused the drainage of a small water body at Clettnadal, exposing deposits of Late Devensian and Holocene age. Pollen, diatom and invertebrate analyses have provided variable records of environmental change during stratigraphical event GI‐1. Event GS‐1 is revealed by the non‐pollen evidence, especially by Coleoptera, by sediment stratigraphy, and by radiocarbon dating. In contrast, the pollen evidence indicates that an arctic tundra flora, in which dwarf shrubs were prominent, persisted throughout the Late‐glacial. The Holocene brought colonisation by tree birch, but by ca. 9000 14C yr BP the taxon had almost disappeared. This contrasts strongly with other Holocene pollen records for Shetland where both Betula and Corylus avellana‐type survived longer—at some sites, for example, until ca. 2900 yr BP. The extreme westerly and exposed coastal situation of Clettnadal appears to be responsible both for a muted Late‐glacial response in the pollen record of terrestrial vegetation and for the early replacement of woodland by a maritime grassland. The results provoke questions concerning biological stability at times of marked climatic change. Copyright © 2003 John Wiley & Sons, Ltd.

Mid-latitude North-Atlantic aerosol characteristics in clean and polluted air

Aerosol number concentrations ( r>1.5 nm) and size distributions (5 nm–150 μm radius) are reported for air masses typical of clean and polluted air masses over a North–East Atlantic coastal site (Mace Head). In clean marine air, total particle concentration is typically 400–600 cm −3, rising to between 600 and 1500 cm −3 for modified maritime air, and in the most polluted air, concentrations increase to ≈7000 cm −3. In all air masses, regular bursts of ultra-fine (1.5–5 nm) particles (UFP) were observed over several hours duration and coincided with low tide occurrence in the presence of solar radiation. During these bursts, measured UFP concentrations exceeded 180,000 cm −3. Typically, the sub-micron marine size distribution possessed a bi-modal shape, typical of cloud-induced aerosol growth, with an accumulation mode centred at 0.1–0.2 μm (radius) and a fine mode ≈0.02 μm, while super-micron sea-spray particles possessed a mode at ≈1–5 μm, extending to ≈10 μm under moderately low wind speeds of 5–6 m s −1. Under higher wind speed conditions (10–11 m s −1), a spume drop mode, extending to sizes of 150 μm, was observed. In anthropogenically influenced air masses, the sub-micron size distribution remained bi-modal, although to a lesser extent. Number concentration is dominated by sub-micron aerosol in all air masses, in marine air masses, surface area is generally dominated by super-micron particles, and volume is overwhelmingly dominated by the mode centred on 10 μm under moderate conditions, and 100 μm under higher winds. By comparison, in polluted air, surface area is dominated by sub-micron sizes and volume dominated by super-micron sizes. After nucleation bursts, growth of new, ultra-fine, particles into sizes in the accumulation mode can be observed under some conditions with growth rates of the order of 10 nm/h. Calculating the pre-existing aerosol condensation sink and the growth rate of newly formed particles allowed estimation of the condensing vapour concentration producing the observed growth along with the source rate of the condensing vapour. The concentration of condensable vapour and its source strength were 10–14×10 7 molecules cm −3 and 3–14×10 5 molecules cm −3 s −1, respectively.

Dental indicators of seasonal hunan presence at the Danish Boreal sites of Holmegaard I, IV and V and Mullerup and the Atlantic sites of Tybrind Vig and Ringkloster

Important new seasonal evidence has been derived from four early Holocene Danish Mesolithic sites based upon tooth-deselopment stages in dentally immature red deer (Cervus elaphus) and roe deer (Capreolus Capreolus). Radiographs of the developing molars aind premolars have been used to provide an indicationl of age at death by comparisons with modem known-age specimens. Knowledge of their age when killed indicates at what time of the year humans were present at the sites. Determining whether a site was occupied seasonally or year-round is critical to subsequent interpretations of human economic and social activity. Based on this new line of enquiry there is strong evidenice for the killing of red aind roe deer during the warmer months of the year at all the Boieal sites. At the Atlantic coastal site of Tybrind Vig red deer were killed in both winteand summer, while at the traditionally winter inland site of Ringkloster esvidence of red deer being killed during the summer months has been found.

Speciation of major arsenic species in seawater by flow injection hydride generation atomic absorption spectrometry.

Arsenic present at 1 microg L(-1) concentrations in seawater can exist as the following species: As(III), As(V), monomethylarsenic, dimethylarsenic and unknown organic compounds. The potential of the continuous flow injection hydride generation technique coupled to atomic absorption spectrometry (AAS) was investigated for the speciation of these major arsenic species in seawater. Two different techniques were used. After hydride generation and collection in a graphite tube coated with iridium, arsenic was determined by AAS. By selecting different experimental hydride generation conditions, it was possible to determine As(III), total arsenic, hydride reactive arsenic and by difference non-hydride reactive arsenic. On the other hand, by cryogenically trapping hydride reactive species on a chromatographic phase, followed by their sequential release and AAS in a heated quartz cell, inorganic As, MMA and DMA could be determined. By combining these two techniques, an experimental protocol for the speciation of As(III), As(V), MMA, DMA and nonhydride reactive arsenic species in seawater was proposed. The method was applied to seawater sampled at a Mediterranean site and at an Atlantic coastal site. Evidence for the biotransformation of arsenic in seawater was clearly shown.

Diurnal cycles of short-lived tropospheric alkenes at a north Atlantic coastal site

Observation of diurnal cycles in atmospheric concentrations of reactive alkenes are reported from measurements performed at a North Atlantic coastal site (Mace Head, Eire 53°19′34″N; 9°54′14″W). Species seen to exhibit distinct cycles included isoprene, ethene, propene, 1-butene, iso-butene and a substituted C 6 alkene. Five hundred and thirty air mass classified measurements were performed over a 4 week period at approximately hourly frequency and demonstrate that during periods when air flow resulted from unpolluted oceanic regions a clear daily cycle in concentrations existed, peaking at around solar noon for all species. These observations support the proposed mechanism of production via photochemical degradation of organic carbon in sea water. The observed concentrations showed strong correlation (propene R 2>0.75) with solar flux, with little relationship to other meteorological or chemical parameters. The species’ short atmospheric lifetimes indicate that the source of emission was from local coastal waters within close proximity of the sampling site. At solar noon concentrations of reactive alkenes from oceanic sources were responsible for up to 88% of non-methane hydrocarbon reaction with the hydroxyl radical at this coastal marine site.

Local meteorological features affecting chemical measurements at a North Atlantic coastal site

One of the foci of the North Atlantic Regional Experiment (NARE) 1993 summer intensive campaign was Chebogue Point, approximately 10 km south of Yarmouth, Nova Scotia. Measurements were taken at this site with a 915‐MHz boundary layer wind profiler, the Canadian Twin Otter and National Center for Atmospheric Research King Air aircraft, and a variety of surface instruments. This paper discusses features observed in the meteorological measurements and the implications of those features for the interpretation of chemical measurements. The meteorology of this coastal site is complex. A strong surface‐based temperature inversion was almost always present, producing strong layering in the lower atmosphere. As a result, surface chemistry measurements were not often representative of the state of the overlying atmosphere. A low‐level jet was also frequently present. A variety of turbulence structures were observed by the profiler, including convective boundary layers and complex layering. Ozone concentrations above 60 parts per billion at the surface occurred on four occasions late in August, in conjunction with strong stability and winds off the Atlantic Ocean (Gulf of Maine). Ozone levels of more than 60 ppbv were observed by the aircraft at altitudes between 400 and 1600 m on five other occasions earlier in the month. Particular (but not necessarily unusual) combinations of transport, mixing, and source conditions appear to be required to produce ozone episodes at Chebogue Point.

Toxic contaminants in rainfall in Canada: 1984

Replicate rain samples for most of the 1984 wetfall season were collected from four widely separated sites in Canada, and concentrations and loadings of a number of polychlorinated biphenyls and organochlorine pesticides were determined for each location. Comparisons were made among the sites and with results from other years. The major contaminants in 1984 were, in order of concentration, α-hexachlorocyclohexane (α-HCH or α-BHC), lindane and polychlorinated biphenyls (PCBs). Found at lower levels were dieldrin, methoxychlor (in the Lake Superior area), DDT residues, endrin (especially at Kouchibouguac), heptachlor epoxide and hexachlorobenzene. The loading of the α-HCH/lindane pair was higher at the Atlantic coastal site than at the other locations, possibly because of the greater precipitation there. No geographic trend for PCBs was apparent. For the other substances, no significant pattern to the differences between sites can be discerned. The qualitative similarities of concentrations and loadings at the widely separated locations, however, suggest long-range atmospheric transport. A comparison between results from two Lake Superior sites indicated no shoreline effect on the concentrations of over-lake versus shoreline samples. The differences observed were in accord with those observed in 1983 and were attributed to lack of replenishment from the lake surface.

Stability of a three‐dimensional foam layer in seawater

There are many dynamic events responsible for the production of a multilayer surface foam in seawater. The residence time of foam at the surface depends on the stability of the bubbles in that foam. This paper examines the stability of three‐dimensional foam layers of various thicknesses produced by blowing air through controlled laboratory samples of simulated seawater and a sample of seawater obtained from an Atlantic coastal site. The results clearly show that for oceanographically relevant salt concentrations between 20 and 36 parts per thousand there are no appreciable changes in the foaming characteristics of seawater due to salinity variations. The stability characteristics of real seawater closely followed those of the simulated seawater. Procedures and equations for estimating thickness variations and lifetimes of foam layers on a saltwater surface are contained in this paper. The results also provide some valuable insights into the influence of organic surface active materials that have been scavenged to the surface by rising bubbles and removed by the bursting process near the surface of a three‐dimensional foam layer.