Paleoclimatic evolution of the Galician continental shelf (NW of Spain) during the last 3000 years: from a storm regime to present conditions
Introduction
Understanding factors affecting climate change in the Holocene is of considerable importance: the topic being the subject of much current research and debate in relation to future climate change. Several climatic oscillations have characterized the last 3000 years. The most important has been identified at the Subboreal/Subatlantic transition, at around 850 cal. BC (van Geel et al., 1996), characterized by a shift from a relatively warm climate to cool and wet conditions in mid-latitudes (Kilian et al., 1995, van Geel et al., 1999). The first warm period in the last 3000 years coincides with the Roman Warm Period peaking at 100 AD (Bianchi and McCave, 1999) with a return to cold conditions after the fifth century in the Dark Ages (Lamb, 1995). In the last millennium, the best identified climatic fluctuations are the Medieval Warm Period (MWP), 900–1250 AD (Lamb, 1995), and the Little Ice Age (LIA), 1350–1800 AD (Stuiver et al., 1995).
These climatic oscillations have been registered by several authors in a large variety of records, for example in Greenland ice cores (Meese et al., 1994, O'Brien et al., 1995, Kreutz et al., 1997, Dahl-Jensen et al., 1998), North Atlantic deep sea cores (Keigwin, 1996, Bond et al., 1997, Bianchi and McCave, 1999), subtropical deep sea cores (deMenocal et al., 2000), lake sediments (Campbell et al., 1998), peat bogs (Barber et al., 2000) and tree rings (Edwards et al., 2000). However, paleoclimate records from shallow marine areas are very scarce. Records from such areas provide decisive information connecting continental with deep sea records. High sedimentation rates in these areas allow for detailed reconstructions in terms of temporal resolution, but the establishment of an accurate chronology in these environments is difficult thus hindering correct interpretation of the sedimentary record.
The present study is based on material from a 96 cm gravity core (CGPL00-1) retrieved from the outer Galician continental shelf (NW of Spain, 42°5′15.115″N, 9°3′46.380″W, 130.8 m water depth, Fig. 1a). Grain size, organic carbon, organic carbon/total nitrogen ratio, biogenic opal and planktonic foraminifera are the main parameters constituting this multiproxy study. The aim of the present work is to integrate these geochemical and micropaleontological proxies in order to reconstruct environmental factors (water dynamics, storminess, water column productivity, etc.) and their evolution during the last 3000 years in the western Galician outer continental shelf.
Section snippets
Regional setting
The study area (Fig. 1a) extends between 41°53′ and 42°53′ latitude N and 8°35′ and 9°32′ longitude W, and represents a climatic province in mid-latitude region, strongly influenced by the position of the polar front. The oceanography of the western Galician coast is affected by wind-driven upwelling that is common along the eastern boundary of the North Atlantic between 10°N and 44°N (Wooster et al., 1976). The seasonal evolution of the Iberian upwelling is closely related to the large-scale
Materials and methods
The gravity core used in this work was recovered on board the B/O Mytilus during a cruise in May 2000. The core was sealed just after collection and kept in storage at 4 °C until analyses were performed in the laboratory. The core was split longitudinally in two sections and 1 cm thick slices were removed for radiographical analyses with a Cabinet X-ray System (Faxitron Series, Hewlett-Packard). After splitting, the core was visually described and sampled. One section was used for
Core description
Gravity core CGPL00-1 presents two well-differentiated sections (Fig. 2a). An intense bioturbation was observed throughout the core, especially in some critical intervals around 80 and 70 cm. The lower half consists mainly of sand overlaying a basal 2 cm interval of bioclastic gravel. Internal laminations were observed in this sandy interval, although sometimes obscured by bioturbation. The lamination is clearly visible on X-ray radiographies from 91 to 79 cm. Glauconite mean percentage in the
Discussion
Sharp lithological contrasts recorded in the core and the trends of most measured variables (TC, TOC, TN, opal and foraminiferal abundance) indicate the existence of two distinct intervals with different environmental conditions in the study region during the last 3000 years. Throughout the sandy interval low TC, TN and opal levels are recorded, whereas in the muddy interval high values of these parameters occur from about 2800 cal. BP to present.
The age model previously discussed indicates
Conclusions
During the last 3000 years, two periods with contrasted environmental conditions have been identified in the western Galician continental shelf. The most pronounced environmental change took place at 2850 cal. BP, coinciding with the Subboreal/Subatlantic transition. This transition represents a climate instability period that was accompanied by high storminess in mid-latitudes. Sedimentation on the western Galician shelf is interpreted to have been controlled by this storm regime. Strong
Acknowledgements
We thank S. Rúa-Santerbás and M. Martínez-García their help with sample processing and the Mytilus crew for help in core collection. A.W. Dale and K. Rea were of great help in making language corrections. We are indebted to M. Pérez-Arlucea for her helpful critical comments on this paper. Very constructive reviews by F.J. Sierro and M. Leeder are sincerely acknowledged. R.G.A. and P.B. acknowledge Ministerio de Educación, Cultura y Deportes and Xunta de Galicia for doctoral grants. This work
References (66)
- et al.
Mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling of the Galician shelf (NW Iberian Peninsula)
Marine Geology
(1997) - et al.
Replicated proxy-climate signals over the last 2000 yr from two distant peat bogs: new evidence for regional palaeoclimate teleconnections
Quaternary Science Reviews
(2000) - et al.
Concentrations and burial fluxes of organic and inorganic carbon on the eastern margins of the Arabian Sea
Marine Geology
(2001) Foraminifera
- et al.
Organic content and preservational controls in surficial shelf and slope sediments from the Arabian Sea (Pakistan margin)
Marine Geology
(1999) - et al.
Benthic foraminifera response to variations in surface water productivity and oxygenation in the northern Arabian Sea
Marine Micropaleontology
(1998) - et al.
δ13C response surface resolves humidity and temperature signals in trees
Geochimica et Cosmochimica Acta
(2000) - et al.
Opal and organic carbon in laminated diatomaceous sediments: Saanich Inlet, Santa Barbara Basin and Miocene Monterey Formation
Marine Geology
(2001) - et al.
Dating raised bogs: new aspects of AMS 14C wiggle matching, a reservoir effect and climate change
Quaternary Science Reviews
(1995) - et al.
Deposition and modification of a flood layer on the northern California shelf: lessons from and about the fate of terrestrial particulate organic carbon
Marine Geology
(1999)
Preservation of elemental and isotopic source identification of sedimentary organic matter
Chemical Geology
A simple method for the rapid determination of biogenic opal in pelagic marine sediments
Deep-Sea Research
Glaucony from the margin off northwestern Spain
Upwelling influence on the Galician coast: silicate in shelf water and underlying surface sediments
Continental Shelf Research
Hidrography of the Artabro Gulf in summer: western coastal limit of Cantabrian seawater and wind-induced upwelling at Prior Cape
Oceanologica Acta
Nutrient dynamics in the Galician coastal area (Nortwestern Iberian Peninsula): do the Rias Bajas receive more nutrient salts than the Rias Altas?
Continental Shelf Research
A review of the Si cycle in the modern ocean: recent progress and missing gaps in the application of biogenic opal as a paleoproductivity proxy
Global and Planetary Change
Water masses in the upper and middle North Atlantic Ocean east of the Azores
Deep-Sea Research
The GISP2 δ18O climate record of the past 16,500 years and the role of the sun, ocean, and volcanoes
Quaternary Research
The role of solar forcing upon climate change
Quaternary Science Reviews
Proximality trends in modern storm sands from the Helgoland Bight (North Sea) and their implications for basin analysis
Senckenbergiana Maritima
An ecological, zoogeographic and taxonomic review of recent planktonic foraminifera
Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland
Nature
Coastal upwelling of the Rías Bajas, Galicia, northwest Spain: I. Hydrographic studies
Rapports et Proces Vervaux des Reunions-CIESM
Size-fractionated primary productivity and biomass in the Galician shelf (NW Spain): net plankton versus nanoplankton dominance
Scientia Marina
A pervasive millenial-scale cycle in North Atlantic Holocene and glacial climates
Science
On the organic carbon maximum on the continental slope of the eastern Arabian Sea
Journal of Marine Research
Late Holocene ∼1500 yr climatic periodicities and their implications
Geology
Paleoceanographic reconstructions from planktonic foraminifera off the Iberian Margin: temperature, salinity and Heinrich events
Paleoceanography
Past temperatures directly from Greenland ice sheet
Science
Coherent high-and low-latitude climate variability during the Holocene warm period
Science
The last 3000 years in the Ría de Vigo (NW Iberian Margin): climatic and hydrographic signals
Holocene
Processes controlling the organic carbon content of open oceans sediments
Paleoceanography
Cited by (45)
Deciphering the lithological consequences of bottom trawling to sedimentary habitats on the shelf
2016, Journal of Marine SystemsTiming of deglaciation and postglacial environmental dynamics in NW Iberia: The Sanabria Lake record
2014, Quaternary Science ReviewsGrain-size effect of biogenic silica in the surface sediments of the East China Sea
2014, Continental Shelf ResearchVolumetric budget calculation of sediment and carbon storage and export for a late Holocene mid-shelf mudbelt system (NW Iberia)
2014, Continental Shelf Research