Environmental controls on modern chironomid faunas from NW Iceland and implications for reconstructing climate change

Reconstructing climate change quantitatively over millennial timescales is crucial for understanding the processes that affect the climate system. One of the best methods for producing high resolution, low error, quantitative summer air temperature reconstructions is through chironomid analyses. We analysed over 50 lakes from NW and W Iceland covering a range of environmental gradients in order to test whether the distribution of the Icelandic chironomid fauna was driven by summer temperature, or whether other environmental factors were more dominant. A range of analyses showed the main environmental controls on chironomid communities to be substrate (identified through loss-on-ignition and carbon content) and mean July air temperature, although other factors such as lake depth and lake area were also important. The nature of the Icelandic landscape, with numerous volcanic centres (many of which are covered by ice caps) that produce large quantities of ash, means that relative lake carbon content and summer air temperature do not co-vary, as they often do in other chironomid datasets within the Arctic as well as more temperate environments. As the chironomid–environment relationships are thus different in Iceland compared to other chironomid training sets, we suggest that using an Icelandic model is most appropriate for reconstructing past environmental change from fossil Icelandic datasets. Analogue matching of Icelandic fossil chironomid datasets with the Icelandic training set and another European chironomid training set support this assertion. Analyses of a range of chironomid-inferred temperature transfer functions suggest the best to be a two component WA-PLS model with r ² _jack = 0.66 and RMSEP = 1.095°C. Using this model, chironomid-inferred temperature reconstructions of early Holocene Icelandic sequences show the magnitude of temperature change compared to contemporary temperatures to be similar to other NW European chironomid sequences, suggesting that the predictive power of the model is good.     

Dissolved and total organic and inorganic carbon in some British rivers

Rivers transport both organic and inorganic carbon from their sources to the sea. Results of ~800 organic and inorganic analyses from various British rivers of contrasting size and land use are presented here: (1) the headwater River Tern, a rural river of 852 km² catchment; (2) the Ouseburn, a small urban 55 km² catchment; (3) the River Tyne, a larger river system of ~3000 km² catchment; (4) a spatial survey from 205 sample sites on ~60 rivers from SW England. We found that, with the exception of peat-rich headwaters, DIC concentration is always greater than DOC. DIC is primarily in the form HCO₃ ⁻ , with DIC concentrations highest in highly urbanised catchments, typically greater than those observed in catchments with carbonate bedrock, demonstrating a significant and previously unrecognised anthropogenic inorganic carbon input to urban rivers.     

A County‐Level Risk Assessment of the Deep Water Horizon Oil Spill in the Gulf of Mexico

This paper undertakes a risk assessment of coastal counties in the Gulf of Mexico impacted by the 2010 Deep Water Horizon oil spill. The study evaluates hazard risk from the perspective of community resilience, social capital, and access to resources. The proposed hazard risk location model re‐specifies risk as a function of hazard, exposure, and coping ability. The model employs an autoregressive function and a threshold analysis to develop a place‐based risk assessment. The results indicate that spatial variation in risk levels coincides with locational differences in social capital across the study area. Geographical proximity to the spill, population density, and unemployment rate are also key factors in determining overall risk. Furthermore, temporal variation in risk levels is determined by exposure to previous hazard events and changes in the business cycle.     

Overestimation of short-term coastal cliff retreat rates in the eastern Mediterranean resolved with a sediment budget approach

Our understanding of sea-cliff erosion processes and their response to recent and/or projected environmental changes such as sea-level rise, climate change and anthropogenic development hinges on our ability to quantify sea-cliff retreat rates and their variability through time. Here, we focus on Israel's Mediterranean ‘Sharon’ sea-cliff as a case study for examining the significance of recent short-term (i.e. annual to decadal) cliff-top retreat rates that appear to exceed longer-term rates of ‘background’ (i.e. centennial to millennial) retreat by 1–2 orders of magnitude. We demonstrate that an inherent sampling bias in rate estimates inferred from observation intervals shorter than process episodicity can also explain such a pattern. This potential ambiguity leads to a striking paradox where despite highly accurate and robust documentation of recent cliff-top retreat, such as that obtained from aerial photographs and/or instrumental surveys, the short-term retreat rates of episodically retreating sea cliffs remain poorly constrained. To address this key data gap along the Sharon sea cliff we employed a sediment budget approach that focuses on quantifying the continuous wave scouring of cliff-collapsed material from the shore platform as a rate-limiting process for episodic retreat of the cliff above. We used four high-resolution (0.5 m/pixel) airborne LiDAR data sets acquired between 2006 and 2015 to determine short-term maximum retreat rates of up to ~0.08 m/yr during this nine-year period. These modern retreat rates compare to the cliff's background retreat rate of 0.03 to 0.09 m/yr since the mid-Holocene, as determined herein from multiple geologic and archeological observations. Our results demonstrate that previously reported twentieth century cliff-top retreat rates for this sea cliff, which range up to values of several meters per year, are biased and that sea-cliff erosion rates have not yet been significantly impacted by recent environmental changes in the eastern Mediterranean basin, such as the restriction of sediment supply following emplacement of the Nile's Aswan dam system. © 2018 John Wiley & Sons, Ltd.     

Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev Desert, Israel

Grain size analyses of three hilltop, primary eolian loess sequences in the Negev desert, southern Israel, show a bimodal grain-size distribution at 50-60 μm and 3-8 μm. Using analyses of mineralogy and OSL ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time, suggesting an enhancement of a time-transgressive proximal dust source compared to a distal, Saharan fine-grain dust. The only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into Sinai and the Negev concurrently with the loess accretion during the late Pleistocene as a result of the exposure of the Mediterranean shelf. We therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea. This relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as Northern Africa, China and Australia.     

Characteristics of alkenones synthesized by a bloom of emiliania huxleyi in the Bering Sea

We investigated the characteristics of the alkenones produced by a bloom of Emiliania huxleyi in the eastern Bering Sea in 2000. Alkenones were detected in surface waters between 57°N and 63°N, where phosphate concentrations were low and the ammonium/nitrate ratio was high. The total alkenone content (C_37:2, C_37:3, and C_37:4) ranged from 22.0 to 349 μg g⁻¹ in suspended particles and from 0.109 to 1.42 μg g⁻¹ in surface sediments. This suggests that a large proportion of the particulate alkenones synthesized in the surface water rapidly degraded within the water column and/or at the water-sediment interface of the Bering Shelf. The change in the stable carbon isotopic composition (δ¹³C) of C_37:3 alkenone could not be explained only by variation in [CO₂(aq)] in the surface water but also depended on the growth rate of E. huxleyi. The alkenone unsaturation index (U^K′₃₇) was converted into an alkenone “temperature” with three equations [Prahl et al 1988], [Sikes et al 1997] and [Müller et al 1998]; Sikes et al.’s (1997) equation gave the best correlation with the observed sea surface temperature (SST) in the eastern Bering Sea. However, some temperatures estimated by Sikes et al.’s (1997) equation from the U^K′₃₇ varied from the observed SST, possibly because of the rapidly changing rate of alkenone synthesis in the logarithmic growth stage or the low rate of alkenone synthesis when nutrients were limiting. Temperatures estimated from U^K′₃₇ in the surface sediments (6.8-8.2°C) matched the observed SST in September (7-8°C) but differed from the annual average SST of 4 to 5°C, suggesting that most of the alkenone in the eastern Bering Sea was synthesized during limited periods, for instance, in September. The relative amounts of C_37:4 alkenone as proportions of the total alkenones (referred to as C_37:4%) were high, ranging from 18.3 to 41.4%. Low-salinity water (<32 psu) within the study area would have contributed to the high C_37:4% because a negative linear relationship between C_37:4% and salinity was found in this study.     

Flow conditions of the 2004 Indian Ocean tsunami in Thailand,inferred from capping bedforms and sedimentary structures

The 2004 Indian Ocean tsunami deposited a sheet of sand with surficial bedforms at the Andaman coast of Thailand. Here we show the recognition of bedforms and the key internal sedimentary structures as criteria of the tsunami supercritical flow condition. The presence of well‐preserved capping bedforms implied a dominant tsunami inflow. Sets of internal sedimentary structures including parallel lamination, seaward and landward inclined‐laminations, and downstream dipping laminae indicated antidune structures that were generated by a supercritical flow current in a depositional stage during the inflow. A set of seaward dipping cross‐laminations containing sand with mud drape on the surface of one depositional layer are a unique indication of an outflow structure. A majority of deposits show normal grading, but in some areas, localized reverse grading was also observed. The recognition of these capping bedforms and determination of the internal sedimentary structures provides new key criteria to help derive a better understanding of tsunami flow conditions.     

Navy sonar and cetaceans: just how much does the gun need to smoke before we act?

Cetacean mass stranding events associated with naval mid-frequency sonar use have raised considerable conservation concerns. These strandings have mostly involved beaked whales, with common pathologies, including "bubble lesions" similar to decompression sickness symptoms and acoustic traumas. However, other cetacean species have also stranded coincident with naval exercises. Possible mechanisms for the strandings include a behavioral response that causes deep divers to alter their diving behavior, which then results in decompression sickness-like impacts. Current mitigation measures during military exercises are focused on preventing auditory damage (hearing loss), but there are significant flaws with this approach. Behavioral responses, which occur at lower sound levels than those that cause hearing loss, may be more critical. Thus, mitigation measures should be revised. A growing number of international bodies recognize this issue and have urged increasing scrutiny of sound-producing activities, but many national jurisdictions have resisted calls for increased protection.