Holocene hydrological changes in the Rhône River (NW Mediterranean) as recorded in the marine mud belt

Abstract

Abstract. Expanded marine Holocene archives are relatively scarce in the Mediterranean Sea because most of the sediments were trapped in catchment areas during this period. Mud belts are the most suitable targets to access expanded Holocene records. These sedimentary bodies represent excellent archives for the study of sea-land interactions and notably the impact of the hydrological activity on sediment accumulation. We retrieved a 7.2 m long sediment core from the Rhône mud belt in the Gulf of Lions in an area where the average accumulation rate is ca. 0.70 m 1000 yr −1 . This core thus provides a continuous and high-resolution record of the last 10 ka cal BP. A multiproxy dataset (XRF core scan, 14 C dates, grain size and organic-matter analysis) combined with seismic stratigraphic analysis was used to document decadal to centennial changes in the Rhône hydrological activity. Our results show that (1) the early Holocene was characterized by high sediment delivery likely indicative of local intense (but short-duration) rainfall events, (2) important sediment delivery around 7 ka cal BP presumably related to increased river flux, (3) a progressive increase in continental/marine input during the mid-Holocene despite increased distance from river outlets due to sea-level rise possibly related to higher atmospheric humidity caused by the southward migration of the storm tracks in the North Atlantic, (4) multidecadal to centennial humid events took place in the late Holocene. Some of these events correspond to the cold periods identified in the North Atlantic (Little Ice Age, LIA; Dark Ages Cold Period) and also coincide with time intervals of major floods in the northern Alps. Other humid events are also observed during relatively warm periods (Roman Humid Period and Medieval Climate Anomaly).

High-resolution Holocene climate and hydrological variability from two major Mediterranean deltas (Nile and Rhone)

“…Land-derived indicators have shown Nile flooding in the first half of the Holocene except around 9200 yr BP when monsoon weakened in response to extratropics forcing. This is in contrast to the steady increase in log(Ti:Ca) ratios in the GoL from early-Holocene to present that suggests an increasing erosion of soil material in the Rhone River watershed (Figure 3f; Bassetti et al, 2016). TERR-alkanes show a similar tendency but stronger fluctuations in the mid-to late-Holocene and a drastic drop around 2500 yr BP (Figure 3e).…”

“…Here, we present a new multi-proxy study that combines sea surface temperatures (SSTs) and land-derived indicators of paleoenvironmental conditions, that is, wax n-alkane biomarkers (thereafter named terrestrial n-alkane (TERR-alkanes)), Ti:Ca ratios, and pollen data preserved in the Nile delta sediments to investigate further this issue. We compare this dataset with the same proxy data from the Rhone River mud belt sediments (NW Mediterranean; Bassetti et al, 2016;Jalali et al, 2016) and speleothem isotope records to evaluate regional pattern and discuss possible mechanisms to explain trans-Mediterranean contrasts.…”

Records of Holocene climatic fluctuations and anthropogenic lead input in elemental distribution and radiogenic isotopes (Nd and Pb) in sediments of the Gulf of Lions (Southern France)

“…Even if accumulation rates are an order of magnitude lower than in estuaries or prodeltas, they generally guarantee more continuous, fine-grained sediment records with minimal hiatuses (see Hanebuth et al, 2015 for a review). The Gulf of Lions mud belt's composition is dominantly supplied by the Rhône River and offers a record of both marine and continental changes documented in three studies that have used Core KSGC-31, namely Bassetti et al (2016), Jalali et al (2016) and Sicre et al (2016). Bassetti et al (2016) documented decadal to centennial changes in Rhône River hydrological activity by using a multiproxy approach (XRF core scan, grain-size and organic-matter analysis) combined with seismic stratigraphy.…”

“…The Gulf of Lions mud belt's composition is dominantly supplied by the Rhône River and offers a record of both marine and continental changes documented in three studies that have used Core KSGC-31, namely Bassetti et al (2016), Jalali et al (2016) and Sicre et al (2016). Bassetti et al (2016) documented decadal to centennial changes in Rhône River hydrological activity by using a multiproxy approach (XRF core scan, grain-size and organic-matter analysis) combined with seismic stratigraphy. While mentioning that more work is needed to unravel anthropogenic from climate control on sedimentation over the late Holocene, the authors came to the conclusion that the elemental composition of marine sediments mainly reflected natural continental erosion and transport.…”

“…Using the same core, Sicre et al (2016) have investigated the Révillon et al (2011). (b) Bathymetric map of the Gulf of Lions, locations of the mud belt (offshore blue facies) and Core KSGC-31 (red star) redrawn after Bassetti et al (2016). The arrow shows the direction of the cross-shelf sediment transport.…”