Impact of atmospheric circulation patterns on coastal dune dynamics, NW Spain

Abstract

Dunes in temperate latitudes have experienced a significant stabilization in recent times, essentially as a consequence of the expansion of dense vegetation cover. Yet, the causes for this gradual stabilization as well as the causes promoting antecedent aeolian mobilization remain poorly understood. The Traba coastal dune field, located in NW Spain, was examined to explore the causes inducing aeolian activity and subsequent stabilization since 1940. Morphological changes were identified through the combination of aerial photographs and geophysical techniques. Local wind field regimes were simulated using a regional climate model to obtain the variability of the most relevant modes of atmospheric circulation in the North Atlantic and European regions; North Atlantic Oscillation (NAO), Eastern Atlantic (EA) and Scandinavian (SCAND). This allows us to identify the impact of these circulation modes over dune dynamics. Results document an episode of aeolian activity during the 1950s followed by a gradual stabilization and fixation of the dune coincident with a decrease on storm and wind intensity. Yet, aeolian sand movement remained active in small areas (blowouts), occurring mainly during the summer. NE winds associated with a negative phase of the EA explain the movement of sand within the dune field under favorable conditions of sand supply. On the other hand, sand supply to the dune field from the beach was promoted by NW winds coincident with the summer negative phase of NAO. During winter, the negative NAO favored frequent SW winds associated with the passage of intense storms, which in turn explain sand remobilization from the beach making sediment available for the NW winds to blow inland. With this work, it is proven that to understand past and future aeolian activity requires critical consideration of the variability and impact of the two principal modes of atmospheric circulation in the North Atlantic (NAO and EA). The SCAND mode explaining a lower percentage of the local wind field variability was also included to achieve higher significance levels of explained variance.

Formation and evolution of back‐barrier perched lakes in rocky coasts: An example of a Holocene system in north‐west Spain

“…A change in diatom assemblages at the topmost part of Unit 6, reflecting the dominance of freshwater euplanktonic diatoms, suggests a recent origin of the very confined environment typical of the present‐day situation. Post‐1950 ad wind speed deceleration and decreased storm activity promoted the progressive expansion of vegetation cover in sand barriers of this coast (González‐Villanueva et al ., ). The recent aggradation in the Doniños dune field could therefore explain the strongly reduced permeability of the barrier at present.…”

“…The north‐west coast of Spain is a mesotidal wave‐dominated coast, with an average tidal range of 2·75 m (maximum 4·40 m; data from Gijón and A Coruña seaports, year 2002). Wind records extending from 1940 to 2001 at A Coruña weather station, which is located 15 km to the south‐west of Doniños, indicate that there are three main wind directions (González‐Villanueva et al ., ): (i) south‐westerly winds associated with the passage of winter storms, which bring high‐energy waves responsible for the offshore–onshore movement of sand on the beach; (ii) medium‐intensity north‐westerly summer winds that transfer sediment from the beach to the adjacent dune system; and (iii) low‐intensity north‐easterly summer winds responsible for sand movement within the dune field. The Doniños system is partially protected from the north‐easterly winds by Monte Lobadiz (30 to 245 m a.m.s.l.).…”

“…In addition to changes in sea‐level and sedimentary budgets, climate variability can also play a significant role, especially in determining the stability of barriers, which are usually vulnerable to strong storm regimes (Andrade et al ., ; Van Vliet‐Lanoë et al ., ). This stability is also a function of changes in the vegetation cover (Jackson & Cooper, ; González‐Villanueva et al ., ) or direct human intervention (Dinis et al ., ).…”

Impact of human activities on coastal vegetation ? A review

“…Aeolian coastal dune systems morphology and plant species composition are the product of complex histories of alternating events of shoreline advance or retreat (González-Villanueva et al, 2013), driven by climate variables, sediment quantity and characteristics, vegetation cover, storm frequency and severity and ocean-level fluctuations (Klijn, 1990;Pye, 1993in González-Villanueva et al, 2013. However, nowadays alteration of the vegetation zonation scheme occurs mostly due to human activities.…”

How did the AD 1755 tsunami impact on sand barriers across the southern coast of Portugal?

“…Geophysical techniques, such as Ground Penetrating Radar (GPR), have been used to explore the internal architecture of coastal barriers allowing the identification and mapping of facies resulting from different processes (Lindhorst et al, 2008;Costas and FitzGerald, 2011;Tamura, 2012;González-Villanueva et al, 2013). Several works have applied this tool to unravel the evolutionary history of coastal barriers and dunes and also to find signatures of abrupt events through the identification of erosive scarps, which are in turn interpreted as the imprints of the impact of past severe events (Buynevich et al, 2007).…”