Abstract
Sea level is a very changeable surface. Furthermore, the land may also be moving, in a slower rate,generating relative sea level changes. The causes of relative sea level changes are variable, but the onesthat cause more intense variations are related to climate.During Little Ice Age (LIA) Northern Hemisphere's summer temperatures fell significantly below theAD 1961–1990 range. This climate situation was responsible for a greater discharge of rivers, whichcould lead to a greater transportation of sediments to the coastline. During these cold periods, sea levelwas lower than in present time. All this could imply a coastline progradation, with the successiveabandon of older beach ridges, reinforcing the sandy supply for dune building. The coastal situationshould be, in some sense, the opposite of the situations that we face today.In present warm period, rivers carry less sediment than during LIA. Moreover, the recent sea level risecontributes to a coastal migration inlands and the erosion of previous beaches and dunes.Our investigation on ancient marine levels and Holocene cemented dunes suggests that the area nearEsmoriz (20 km south of Porto, NW Portuguese coast) is probably subsiding. This possible subsidence,together with recent sea level rise, induced by the end of LIA, could explain the severe coastal erosionthat is taking place at Espinho area (15 km south of Porto) since the middle of the XIX century.This example shows clearly the complexity of relative sea-level changes. Because of this complexity,sea level curves are not similar worldwide, as they depend on the interference of multiple time-scalesphenomena.
Highlights
THE LITTLE ICE AGEThe climatic variations of the last millennia have usually been related to the advances and retreats of alpine glaciers (Fig. 1)
Mörner’s curve (1973) (Fig. 7) shows precisely a rising sea level departing from a low stand around 1830, which coincides with Dalton sunspot minimum and one of the last cold advances of Little Ice Age (LIA)
Espinho has suffered from severe erosion since, at least, 1869 (FERREIRA DINIZ, 1909)
Summary
The climatic variations of the last millennia have usually been related to the advances and retreats of alpine glaciers (Fig. 1). The term “Little Ice Age” (LIA) is generally employed to describe the period of glacial advance of the last few centuries. Sometimes, the term refers only to the period from 1550 to 1800 (LAMB 1977, in GROVE, 1988) This climate episode was characterized by a stronger snowfall in winter and both facts are responsible for a general advance of alpine glaciers (MATTHEWS & BRIFFA, 2005) (Fig. 1). In Brádzil (2005) we can find an excellent state of the art of this complex and interesting matter It is an exhaustive paper about the use of proxies, their limitations and the authors that made important contributions on last millennia climate change. Its end seems quite clear: after 1850, temperatures augmented and we arrive to the actual warm period, clearly contrasting with LIA episode
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