Response of benthic species to post-glacial sea-level rise on the northern Adriatic shelf revealed by stratigraphic unmixing of fossil assemblages

2020 ◽  
Author(s):  
Rafał Nawrot ◽  
Daniele Scarponi ◽  
Adam Tomašových ◽  
Michał Kowalewski
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Age Distribution ◽  
Ecosystem Dynamics ◽  
Time Averaging ◽  
Burial Depth ◽  
Shelf Area ◽  
Benthic Species ◽  
Northern Adriatic ◽  
Fossil Assemblages

<p>Late Quaternary fossil record offers a window into ecosystem dynamics during episodes of abrupt climate warming and sea-level rise following the Last Glacial Maximum, but in marine settings ecological inferences might be hindered by high time-averaging affecting transgressive deposits. However, the signature of temporal shifts in local skeletal production rates may be preserved in the age-frequency distributions (AFDs) of death assemblages. We use carbonate-target radiocarbon ages of 191 shells to examined variation in AFDs among four bivalves species collected from a 2.3-meter-long core recording the post-glacial transgression on the northern Adriatic shelf over the last the last ~14,500 yr.</p><p>The scale of time-averaging within species (interquartile age range) varied from 200 to 7,400 yrs, while the between-species age offsets (differences between the median ages of species) ranged from ~2 to 6,400 yrs within 5-cm-thick core intervals. Although the median ages of <em>Varicorbula</em>, <em>Timoclea</em> and <em>Parvicardium</em> increased with increasing burial depth, shells of <em>Lentidium</em> appeared age-homogeneous throughout the core. Age unmixing revealed a single massive peaks in the abundance of this opportunistic, shoreface species around 14 cal ka BP, coincident with the initial marine flooding of this shelf area during the melt-water pulse 1A. Moreover, a prominent gap in the AFDs between 11 and 12.5 cal ka BP corresponds to a minor sea-level fall associated with the Younger Dryas cold spell. Importantly, the reconstructed onsets and durations of shell production pulses across the four species are consistent with independently-derived relative sea-level history at the site. The species gradually replaced each other through time as the dominant component of the assemblage in accordance with their bathymetric preferences estimated from surveys of the modern Adriatic benthic fauna.</p><p>The diachronous production histories of four bivalve species coupled with subsequent exhumation of old shells and burial of younger shells through bioturbation and sediment reworking resulted in the ecologically mixed fossil assemblages. These assemblages are thus characterized by multi-modal age distribution and millennial-scale age offsets between species co-occurring in the same stratigraphic increments. Although this stratigraphic homogenization and disorder greatly limits the resolution of the raw stratigraphic record, our results demonstrate the power of AFDs to capture shifts in abundance of benthic species during recent episodes of rapid sea-level rise. Fossil assemblages from transgressive deposits preserved on continental shelves represent a rich and underutilized source of data on long-term biotic responses to global climate change and associated shifts in sea level.</p>

Multiple drivers of extreme sea levels in the northern Adriatic Sea

2021 ◽  
Author(s):  
Christian Ferrarin ◽  
Piero Lionello ◽  
Mirko Orlic ◽  
Fabio Raicich ◽  
Gianfausto Salvadori
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Adriatic Sea ◽  
Driving Factors ◽  
Northern Adriatic Sea ◽  
Relative Sea Level ◽  
Northern Adriatic ◽  
Sea Levels ◽  
Extreme Sea Levels ◽  
Relative Sea Level Rise

<p><span><span>Extreme sea levels at the coast result from the combination of astronomical tides with atmospherically forced fluctuations at multiple time scales. Seiches, river floods, waves, inter-annual and inter-decad</span></span><span><span>al dynamics and relative sea-level rise can also contribute to the total sea level. While tides are usually well described and predicted, the effect of the different atmospheric contributions to the sea level and their trends are still not well understood. Meso-scale atmospheric disturbances, synoptic-scale phenomena and planetary atmospheric waves (PAW) act at different temporal and spatial scales and thus generate sea-level disturbances at different frequencies. In this study, we analyze the 1872-2019 sea-level time series in Venice (northern Adriatic Sea, Italy) to investigate the relative role of the different driving factors in the extreme sea levels distribution. The adopted approach consists in 1) isolating the different contributions to the sea level by applying least-squares fitting and Fourier decomposition; 2) performing a multivariate statistical analysis which enables the dependencies among driving factors and their joint probability of occurrence to be described; 3) analyzing temporal changes in extreme sea levels and extrapolating possible future tendencies. The results highlight the fact that the most extreme sea levels are mainly dominated by the non-tidal residual, while the tide plays a secondary role. The non-tidal residual of the extreme sea levels is attributed mostly to PAW surge and storm surge, with the latter component becoming dominant for the most extreme events. The results of temporal evolution analysis confirm previous studies according to which the relative sea-level rise is the major driver of the increase in the frequency of floods in Venice over the last century. However, also long term variability in the storm activity impacted the frequency and intensity of extreme sea levels and have contributed to an increase of floods in Venice during the fall and winter months of the last three decades.</span></span></p>

scholarly journals Abrupt rise in atmospheric CO<sub>2</sub> at the onset of the Bølling/Allerød: in-situ ice core data versus true atmospheric signals

2011 ◽  
Vol 7 (2) ◽  
pp. 473-486 ◽  
Author(s):  
P. Köhler ◽  
G. Knorr ◽  
D. Buiron ◽  
A. Lourantou ◽  
J. Chappellaz
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Radiative Forcing ◽  
Ice Core ◽  
Age Distribution ◽  
Ice Cores ◽  
Rate Of Change ◽  
Atmospheric Co2 ◽  
Abrupt Rise

Abstract. During the last glacial/interglacial transition the Earth's climate underwent abrupt changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A was accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is a matter of current debate. In-situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10 ± 1 ppmv in 230 yr at the same time. Allowing for the modelled age distribution of CO2 in firn, we show that atmospheric CO2 could have jumped by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 greater than the CO2 signal recorded in-situ in EDC. This rate of change in atmospheric CO2 corresponds to 29–50% of the anthropogenic signal during the last 50 yr and is connected with a radiative forcing of 0.59–0.75 W m−2. Using a model-based airborne fraction of 0.17 of atmospheric CO2, we infer that 125 Pg of carbon need to be released into the atmosphere to produce such a peak. If the abrupt rise in CO2 at the onset of the B/A is unique with respect to other Dansgaard/Oeschger (D/O) events of the last 60 kyr (which seems plausible if not unequivocal based on current observations), then the mechanism responsible for it may also have been unique. Available δ13CO2 data are neutral, whether the source of the carbon is of marine or terrestrial origin. We therefore hypothesise that most of the carbon might have been activated as a consequence of continental shelf flooding during MWP-1A. This potential impact of rapid sea level rise on atmospheric CO2 might define the point of no return during the last deglaciation.

scholarly journals Rapid changes in ice core gas records – Part 2: Understanding the rapid rise in atmospheric CO<sub>2</sub> at the onset of the Bølling/Allerød

2010 ◽  
Vol 6 (4) ◽  
pp. 1473-1501 ◽  
Author(s):  
P. Köhler ◽  
G. Knorr ◽  
D. Buiron ◽  
A. Lourantou ◽  
J. Chappellaz
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Core ◽  
Age Distribution ◽  
Ice Cores ◽  
Atmospheric Co2 ◽  
Current Debate ◽  
Last Deglaciation ◽  
Rapid Changes

Abstract. During the last glacial/interglacial transition the Earth's climate underwent rapid changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A is accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is matter of current debate. In situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10±1 ppmv in 230 yr at the same time. Allowing for the age distribution of CO2 in firn we here show, that atmospheric CO2 rose by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 larger than the CO2 signal recorded in situ in EDC. Based on the estimated airborne fraction of 0.17 of CO2 we infer that 125 Pg of carbon need to be released to the atmosphere to produce such a peak. Most of the carbon might have been activated as consequence of continental shelf flooding during MWP-1A. This impact of rapid sea level rise on atmospheric CO2 distinguishes the B/A from other Dansgaard/Oeschger events of the last 60 kyr, potentially defining the point of no return during the last deglaciation.

scholarly journals Historical and recent sea level rise and land subsidence in Marina di Ravenna, northern Italy

2016 ◽  
Vol 59 (5) ◽  
Author(s):  
Ines Cerenzia ◽  
Davide Putero ◽  
Flavio Bonsignore ◽  
Gaia Galassi ◽  
Marco Olivieri ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Land Subsidence ◽  
Adriatic Sea ◽  
Sea Level Change ◽  
Northern Adriatic Sea ◽  
Relative Sea Level ◽  
Northern Adriatic ◽  
Level Change ◽  
Rate Of Increase

The regions facing the northern Adriatic Sea are particularly vulnerable to sea-level rise. Several trade ports are located there, and the area is important from social and economical viewpoints. Since tourism and cultural heritage are a significant source of income, an increase in sea-level could hinder the development of these regions. One of the longest sea-level time series in the northern Adriatic, which goes back to the late 1880s, has been recorded at Marina di Ravenna, in Emilia-Romagna region. The record is anomalous, showing a rate of increase that largely exceeds that observed in nearby stations. During the last few decades, geodetic campaigns based on geometric high precision leveling, SAR interferometry, and GPS have monitored the Ravenna area. In this work, tide gauge observations are merged with yet unpublished geodetic data, aiming at a coherent interpretation of vertical land movements. We confirm that land subsidence is the major cause of relative sea-level change at Marina di Ravenna, at least during the period allowing  for a quantitative analysis (1990-2011). The rate of absolute sea-level change (2.2±1.3 mm yr−1 during the same time period), given by the difference between the rate of relative sea-level change and the rate of subsidence, is consistent with the rate of absolute sea-level change observed by altimetry in the northern Adriatic Sea.

Coastal landforms evolution during the Holocene marine transgression: a witness from the past to understand the future

2020 ◽  
Author(s):  
Livio Ronchi ◽  
Alessandro Fontana ◽  
Annamaria Correggiari
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Coastal Plain ◽  
Adriatic Sea ◽  
Tidal Inlets ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
Marine Transgression ◽  
Coastal Landforms ◽  
Lagoon Systems

&lt;p&gt;The continental shelves submerged during the last marine transgression could constitute a unique laboratory to analyse how coastal landforms developed and evolved within the framework of a rising sea level. Such features therefore represent precious witnesses in the light of the high rates of sea-level rise predicted for the end of the century. Unfortunately, the majority of the coastal landforms have been wiped away during and soon after their submersion as a consequence of the pervasive wave and tidal action. Therefore, only few examples of well-preserved submerged coastal landforms are available.&lt;/p&gt;&lt;p&gt;In this study we focused our attention on the Italian side of northern Adriatic Sea, where a wide, low-gradient continental shelf, coupled to a very rapid marine ingression, allowed the partial conservation of the transgressive coastal landforms. Such study was carried out through the analysis of almost 10,000 km of high-resolution geophysical surveys (CHIRP-sonar profiles) and tens of stratigraphic cores carried out in the area during the last 30 years.&lt;/p&gt;&lt;p&gt;We recognized a series of almost 100 remnants of paleo tidal inlets which formed during the post-LGM transgression that led to the submersion of the Adriatic shelf. Despite paleo tidal inlets are often almost completely erased by the wave ravinement processes, when preserved they represent ideal markers for reconstructing the timing and impact of sea-level rise on the transgressed coastal plain. A wealth of information can be obtained by their analysis, such as the paleo coastlines locations, the dimensions of the paleo lagoon systems and, in particular conditions, the relative paleo sea-level. Such features therefore represent valid means to reconstruct the impact of the transgressive sea on the coastal area.&lt;/p&gt;&lt;p&gt;In particular, the paleo tidal inlets recognized in the northern Adriatic Sea suggest the recurrent formation followed by rapid overstepping of large lagoon systems during the early Holocene. Moreover, these features can be subdivided into clusters based on the depth of their top, thus allowing to infer the position of a series of paleo coastlines and suggesting the occurrence of periods of stasis of the relative sea-level rise, which allowed the formation of such inlets.&lt;/p&gt;&lt;p&gt;Although remnants of paleo tidal inlets are common on the northern Adriatic Shelf, they are almost absent in the northernmost portion of the basin (i.e. the Gulf of Trieste), where a series of paleo fluvial systems have been identified, thus providing a direct witness on the evolution of the coastal plain during a transgressive phase and right before its rapid submersion.&lt;/p&gt;&lt;p&gt;This research provides new insights on two main topics: i) it improves our knowledge on the post-LGM marine transgression, therefore contributing to reconstruct the history of sea-level rise and to constrain the modelling of future behaviour; ii) it contributes to understand the evolution of tidal inlets and lagoon-barrier island systems under the forcing of high rates of sea-level rise.&lt;/p&gt;

Basin-wide homogenization of soft-bottom benthic communities in the wake of anthropogenic habitat degradation in the northern Adriatic Sea

2020 ◽  
Author(s):  
Martin Zuschin ◽  
Alexandra Haselmair ◽  
Ivo Gallmetzer ◽  
Anna Wieser ◽  
Adam Tomasovych
Keyword(s):  
Sea Level ◽  
Adriatic Sea ◽  
Human Impacts ◽  
Benthic Communities ◽  
Sediment Cores ◽  
Time Averaging ◽  
Sedimentation Rates ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
Anthropogenic Habitat

&lt;p&gt;We studied the origin and collapse of Holocene benthic baseline communities in the northern Adriatic Sea from sediment cores and surface grab samples at eight widely spaced sites. They cover areas with sedimentation rates spanning two orders of magnitude, with different nutrient input and with different degrees of time-averaging, ranging from decadal to millennial temporal resolution. Data from sediment cores indicate that during the transgressive phase and maximum flooding, sea-level and establishment of the modern circulation pattern determined the development of benthic communities in shallow-water, vegetated habitats with epifaunal biostromes and, in deeper waters, with bryozoan meadows. After sea-level stabilization, the composition of these baseline communities remained relatively uniform and started to change markedly only with the intensification of human impacts in the late highstand, leading to a dominance of infauna and a decline of epifauna at all sites. This profound ecological change reduced species richness, increased the abundance of infaunal suspension feeders, and led to a decline of grazers and deposit feeders. Live-dead data from grab samples give deeper insight into the degree of anthropogenic impact in historical times. At all sites the living assemblages differ strongly from the death assemblages. At some sites from oligotrophic settings with low sedimentation rates, a total overturn in the community composition is obvious: formerly abundant species have disappeared completely, while the living assemblage is numerically dominated by species that were not present before. Even at sites, which are characterized by physically stressful conditions (i.e., high sedimentation rates in the Po delta), some species that were abundant in the death assemblage have totally disappeared from the living assemblage. Comparison with the dataset from sediment cores documents the recent establishment of an impoverished community, which has no analogue in the Holocene history of the northern Adriatic Sea.&lt;/p&gt;

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