Modern morpho-sedimentological patterns in a tide-dominated estuary system: the Bay of Brest (west Britanny, France)

Gregoire, Gwendoline; Ehrhold, Axel; Roy, Pascal Le; Jouet, Gwénaël; Garlan, Thierry

doi:10.1080/17445647.2016.1139514

Cited by 19 publications

(31 citation statements)

References 25 publications

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“…Bathymetry highlights submarine channels in the Bay of Brest that attest to palaeo-fluvial systems ( Fig. 1a; Gregoire et al, 2016). Palaeo-channels of the two main current rivers, the Aulne and Elorn, are about 30 and 15 m deep respectively, and converge in the west at a trough of about 50 m deep (Troadec et al, 1997).…”

Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

“…Today, the Bay of Brest is characterized by a macrotidal influence with a maximum tidal amplitude of 8m (Troadec et al, 1997). Granulometry of modern sediments reflects specific hydrodynamic conditions mainly related to tidal currents (Gregoire et al, 2016). In its westernmost part, the Bay of Brest is connected to the Atlantic Ocean through the "Goulet", a strait of about 1.8 km large and 50 m deep.…”

Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

“…Marine waters flow into the Bay of Brest at each new tidal cycle with a current speed reaching 1 m/s, mainly oriented S-E. In the stream direction, sedimentation is mainly composed of sands and gravels (Gregoire et al, 2016). On either side of this axis, the current speed is strongly reduced and grain-size is characterized by fine to very fine sediments (silts and clays) in small bays (Troadec et al, 1997;Gregoire et al, 2016).…”

Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

“…In the stream direction, sedimentation is mainly composed of sands and gravels (Gregoire et al, 2016). On either side of this axis, the current speed is strongly reduced and grain-size is characterized by fine to very fine sediments (silts and clays) in small bays (Troadec et al, 1997;Gregoire et al, 2016). The lack of interbedded sands and high energetic sedimentary structures in these bays argues for in situ deposits, an assumption reinforced by 210 Pb profiles carried out on modern sediments (Gregoire et al, 2016Klouch et al, 2016b).…”

Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

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Human-induced river runoff overlapping natural climate variability over the last 150 years: Palynological evidence (Bay of Brest, NW France)

Lambert

Penaud

Vidal

et al. 2018

Global and Planetary Change

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For the first time a very high resolution palynological study (mean resolution of 1 to 5 years) was carried out over the last 150 years in a French estuarine environment (Bay of Brest; NW France), allowing direct comparison between the evolution of landscapes, surface water, and human practices on Bay of Brest watersheds, through continental (especially pollen grains) and marine (phytoplanktonic microalgae: cysts of dinoflagellates or dinocysts) microfossils. Thanks to the small size of the watersheds and the close proximity of the depositional environment to the mainland, the Bay of Brest represents an ideal case study for palynological investigations. Palynological data were then compared to published palaeo-genetic analyses conducted on the same core and to various available instrumental data, allowing us to better characterize past environmental variability since the second half of the 19th century in Western Brittany. We provide evidence of some clues of recent eutrophication and/or pollution that affected phytoplankton communities and which appears linked with increased runoff (higher precipitations, higher percentages of riparian forest pollen, decline of salt marsh-type indicators, and higher values of the XRF Ti/Ca signal), mainly explained by the evolution of agricultural practices since 1945 superimposed on the warming climate trend. We assume that the significant relay observed between dinocyst taxa: Lingulodinium machaerophorum and Spiniferites bentorii around 1965 then followed by Spiniferites membranaceus after 1985, attests to a strong and recent eutrophication of Bay of Brest surface waters induced by high river runoff combined with abnormally elevated air temperatures, especially obvious in the data from 1990. The structure of the dinocyst community has thus been deeply altered, accompanied by an unprecedented increase of Alexandrium minutum toxic form at the same period, as confirmed by the genetic quantification. Despite this recent major anthropogenic forcing, the fossil pollen sequence also records natural climate variability. We highlight, for the first time, a possible connection between climate (AMO modes) and fossil pollen records (especially tree pollination rates) in coastal sediments using tree percentage fluctuations as an indirect Highlights ► High resolution palynological study (last 150 yrs) in a French estuary ► Increased runoff on mainland since 1945 ► Increased eutrophication indices since 1980 ► Changes in phytoplankton communities and increased toxic algal blooms ► Connection between AMO modes and fossil pollen records (tree pollination rates)

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Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

Section: Geomorphological and Geographical Contextsmentioning

confidence: 99%

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Human-induced river runoff overlapping natural climate variability over the last 150 years: Palynological evidence (Bay of Brest, NW France)

Lambert

Penaud

Vidal

et al. 2018

Global and Planetary Change

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“…This may be explained by a tidal reworking within a confined basin of extra-basinally sourced flash flood deposits (Zuchuat et al, 2018), that may have originated from the neighbouring, uplifted Uncompahgre Terraces to the east (Otto & Picard, 1976;Scott et al, 2001), and/or from uplifted highlands to the west (Anderson, 2015;Thorman, 2011). Similar gravel to pebble to cobble sized conglomeratic bedforms are found in modern, tidally influenced and confined basins, such as the Bay of Fundy Shaw et al, 2014;, the San Francisco Bay (Barnard, Hanes, Rubin, & Kvitek, 2006) or the bay of Brest (Gregoire, Ehrhold, Le Roy, Jouet, & Garlan, 2016). Alternatively, conglomeritic channels and dunes may result from the influx of a coarser sediment as short-lived regressive pulses brought material from the proximal part of the basin into distal areas, and regressive pulses are notable during the development of the uppermost parasequence P3 (Zuchuat et al, 2018).…”

Section: Facies Distribution Energy Levels Basin Geometry and Tidmentioning

confidence: 76%

Overprinted allocyclic processes by tidal resonance in an epicontinental basin: The Upper Jurassic Curtis Formation, east‐central Utah, USA

Zuchuat

Sleveland

Pettigrew

et al. 2019

The Depositional Record

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Modern, tide‐dominated and tide‐influenced coastlines are characterized by a range of environments, including deltas, estuaries and lagoons. However, some tide‐dominated basins and related sedimentary units in the rock record, such as the semi‐enclosed, shallow, Utah–Idaho Trough foreland basin of the Jurassic Curtis Sea, do not correspond to any of these modern systems. Persistent aridity caused the characteristic severe starvation of perennial fluvial input throughout this basin, in which the informal lower, middle and upper Curtis, as well as the underlying Entrada Sandstone, and the overlying Summerville Formation were deposited. Wave energy was efficiently dissipated by the shallow basin's elongated morphology (approximately 800 × 150 km), as its semi‐enclosed morphology further protected the system from significant wave impact. Consequently, the semi‐enclosed, shallow‐marine system was dominated by amplified tidal forces, resulting in a complex distribution of heterolithic deposits. Allocyclic forcing strongly impacted upon the system's intrinsic autocyclic processes as the lower Curtis was deposited. Short‐lived relative sea‐level variations, along with uplift and deformation episodes, resulted in the accumulation of three parasequences, each separated by traceable flooding and ravinement surfaces. The subsequent transgression, which defines the base of the middle Curtis, allowed for the shallow‐marine part of the system to enter into tidal resonance as a consequence of the flooded basin reaching the optimal configuration of approximately 800 km in length, corresponding to an odd multiple of the quarter of the tidal wavelength given an average minimum water depth of 20–25 m. This resonant system overprinted the effects of allocyclic forcing and related traceable stratigraphic surfaces. However, the contemporaneous and neighbouring coastal dune field sedimentary rocks of the Moab Member of the Curtis Formation, characterized by five stacked aeolian sequences, as well as the supratidal deposits of the Summerville Formation, lingered to record allocyclic signals, as the Curtis Sea regressed. This study shows that a tide‐dominated basin can enter into tidal resonance as it reaches its optimal morphological configuration, leading to the overprinting of otherwise dominant allocyclic processes by autocyclic behaviour. It is only by considering the sedimentological relationships of neighbouring and contemporaneous depositional systems that a full understanding of the dynamic stratigraphic history of a basin alternatively dominated by autocyclic and allocyclic processes can be achieved.

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Sponge contribution to the silicon cycle of a diatom‐rich shallow bay

López‐Acosta

Maldonado

Grall

et al. 2022

Limnology & Oceanography

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In coastal systems, planktonic and benthic silicifiers compete for the pool of dissolved silicon, a nutrient required to make their skeletons. The contribution of planktonic diatoms to the silicon cycle in coastal systems is often well characterized, while that of benthic silicifiers such as sponges has rarely been quantified. Herein, silicon fluxes and stocks are quantified for the sponge fauna in the benthic communities of the Bay of Brest (France). A total of 45 siliceous sponge species living in the Bay account for a silicon standing stock of 1215 tons, while that of diatoms is only 27 tons. The silicon reservoir accumulated as sponge skeletons in the surface sediments of the Bay rises to 1775 tons, while that of diatom skeletons is only 248 tons. These comparatively large stocks of sponge silicon were estimated to cycle two orders of magnitude slower than the diatom stocks. Sponge silicon stocks need years to decades to be renewed, while diatom turnover lasts only days. Although the sponge monitoring over the last 6 yr indicates no major changes of the sponge stocks, our results do not allow us to conclude if the silicon sponge budget of the Bay is at steady state, and potential scenarios are discussed. The findings buttress the idea that sponges and diatoms play contrasting roles in the marine silicon cycle. The budgets of these two major silicon users need to be integrated and their connections revealed, if we aim to improve our understanding of the silicon cycling in coastal ecosystems.

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Modern morpho-sedimentological patterns in a tide-dominated estuary system: the Bay of Brest (west Britanny, France)

Cited by 19 publications

References 25 publications

Human-induced river runoff overlapping natural climate variability over the last 150 years: Palynological evidence (Bay of Brest, NW France)

Human-induced river runoff overlapping natural climate variability over the last 150 years: Palynological evidence (Bay of Brest, NW France)

Overprinted allocyclic processes by tidal resonance in an epicontinental basin: The Upper Jurassic Curtis Formation, east‐central Utah, USA

Sponge contribution to the silicon cycle of a diatom‐rich shallow bay

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