Using Distributed Temperature Sensing for Long-Term Monitoring of Pockmark Activity in the Gulf of Patras (Greece): Data Processing Hints and Preliminary Findings.

Patras Gulf pockmark field (Western Greece) is a tectonically controlled field that has been activated at least twice by strong earthquakes (M5.4, 14 July 1993 and M6.4, 8 June 2008), and episodic gas seepages have been recorded in the past using geophysical means. A distributed temperature sensor (DTS) system was deployed inside a shallow pockmark and along an active fault at the northern end of the field. This ongoing experiment represents the first long-term monitoring ever conducted on gas-bearing pockmarks and active faults by the DTS system. For now, we have acquired and analyzed data regarding about 1.56 years. One of the primary objectives of this study is to establish methodological queues for data processing and analysis, including spectral analysis and incomplete data treatment techniques, to be standardized for use in further stages of the experiment. Spectral analysis was proven capable of separating the temperature footprint of background environmental components, such as sea-atmosphere heat flux, tides, and winds/waves, from high-frequency temperature residuals. Those residuals represent unusual events that might be correlated to seismicity. Monitoring the causal relationship between seismic activity and seabed water temperature changes in the field was thus attempted. No significant local earthquakes occurred during the monitoring period. Although the relation between seismicity and irregular seabed water temperature events was not systematic, we postulate that four thermal events have a causative link with the local seismicity. The DTS system constitutes a low-cost monitoring system, and the promising preliminary results of this experiment suggest that it is worth testing for a longer period.

COVID-19-related litter pollution on Greek beaches and nearshore shallow water environments.

COVID-19 pandemic has led to an increase in certain types of litter, many of which are expected to end up in the marine environment. The present study aimed to monitor the pandemic-related litter pollution along the Greek coastal environment. Overall, 59 beach and 83 underwater clean-ups were conducted. Litter was categorized as: PPE (face masks and gloves), COVID-19-related, single-use plastic (SUP) and takeaway items. PPE, dominated by face masks (86.21 %), accounted for 0.29 % of all litter. The average PPE density was 3.1 × 10-3 items m-2 and 2.59 items/ 100 m. COVID-19-related items represented 1.04 % of the total. Wet wipes showed higher densities (0.67 % of all litter) than in the pre-COVID era, while no increase in SUP and takeaway items was observed. Benthic PPE, dominated by gloves (83.95 %), represented 0.26 % of the total. The mean PPE density was 2.5 × 10-3 items m-2.

Insights into seafloor litter spatiotemporal dynamics in urbanized shallow Mediterranean bays. An optimized monitoring protocol using towed underwater cameras.

Monitoring of marine litter at the sea surface, the beaches and the seafloor is essential to understanding their sources, pathways and sinks and design effective clean-up programs or increase public awareness for reducing litter waste. Up until today, seafloor litter is the least exploited component of marine litter. Although the protocols for recording and assessing seafloor litter in the deep-sea environments are currently being actively defined and practiced, shallow seafloor litter survey protocols are still notably under-developed. Moreover, trawling for fishing, which is the main means for collecting seafloor litter data, needs to be phased out in the coming years due to its high environmental footprint and be replaced by less destructive ways based on underwater imagery. In this paper we propose an integrated approach for assessing in detail the spatiotemporal distribution and composition of seafloor litter in shallow coastal environments, using common towed underwater cameras. Effort has been put to correctly estimating spatial litter densities regarding the true coverage of the visualized area, which was efficiently extracted through photogrammetric reconstruction of the seafloor. Interpretation of the spatial distribution of litter was aided by auxiliary bathymetric and swath sonar backscatter datasets, to determine the seabed geomorphological features that control their dispersion and composition. Local geo-morphology, along with any reported coastal anthropogenic activity, are correlated to seafloor litter densities to investigate the temporal and spatial dynamics that control their distribution and temporal trends in Syros Island, Cyclades, Greece. There, in the context of LIFE DEBAG project, monitoring of an urbanized shallow bay for 3 consecutive years has been performed to assess the impact of an intensive local awareness raising campaign to the local environment. A significant reduction of litter densities under the impact of this campaign has been documented, while links between the seafloor litter transport dynamics and the seabed micro- and macro-topography were made evident. Monitoring litter densities on the seafloor of urbanized shallow bays proved to be a prospective way of tracking marine litter pressures on the local marine environment.

Spatiotemporal assessment of the environmental quality of bottom waters through the study of benthic foraminifera in a semi-enclosed gulf.

The evolution of the bottom water in Amvrakikos Gulf in Ionian Sea at western Greece for a 50-year timespan was assessed by benthic foraminifera assemblages. The degradation of the bottom water of Amvrakikos has been a catalyst for the surface water degradation. The east basin has shown permanent low environmental quality in bottom waters since 1980, while the west basin has been under seasonal hypoxic regime since 2000. The most adverse environmental conditions occurred in 1990-2000 and 2005-2010 coinciding with the recorded fish mortality events. The major cause of the environmental quality improvement of the bottom water is the intrusion of seawater. In western areas of the gulf, where the influence of the seawater is high, the decreased temperature improves the environmental conditions, while in the areas influenced by river discharges (east and northern), the environmental conditions are depended on multiple causes like organic matter input and surface salinity.

Author Correction: High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift.

Young rifts are shaped by combined tectonic and surface processes and climate, yet few records exist to evaluate the interplay of these processes over an extended period of early rift-basin development. Here, we present the longest and highest resolution record of sediment flux and paleoenvironmental changes when a young rift connects to the global oceans. New results from International Ocean Discovery Program (IODP) Expedition 381 in the Corinth Rift show 10s-100s of kyr cyclic variations in basin paleoenvironment as eustatic sea level fluctuated with respect to sills bounding this semi-isolated basin, and reveal substantial corresponding changes in the volume and character of sediment delivered into the rift. During interglacials, when the basin was marine, sedimentation rates were lower (excepting the Holocene), and bioturbation and organic carbon concentration higher. During glacials, the basin was isolated from the ocean, and sedimentation rates were higher (~2-7 times those in interglacials). We infer that reduced vegetation cover during glacials drove higher sediment flux from the rift flanks. These orbital-timescale changes in rate and type of basin infill will likely influence early rift sedimentary and faulting processes, potentially including syn-rift stratigraphy, sediment burial rates, and organic carbon flux and preservation on deep continental margins worldwide.