Presentation on theme: "The Littorina transgression in southeastern Sweden and its relation to mid-Holocene climate variability SHI-YONG YU GeoBiosphere Science Centre Department."— Presentation transcript:
The Littorina transgression in southeastern Sweden and its relation to mid-Holocene climate variability SHI-YONG YU GeoBiosphere Science Centre Department of Geology/Quaternary Sciences Lund University Sölvegatan 12 SE LUND Supervisors P. Sandgren, B. E. Berglund and L. Barnekow
What are sea-level changes? Sabadini, 2002 Sea level is the location where ocean water intercepts the land Sea-level changes are the result of the complex feedback among the Earths different spheres at variable response time scales
Future sea-level rise: an enigma Munk, 2002 Cabanes et al., 2001 Sea-level history over the last 100 years was well recorded by tide gauges (2 mm/yr). An acceleration was observed over the last decade (3 mm/yr). Other components involved in this complex pattern are unclear.
The best prophet of the future is the past To give a credible scenario of future sea-level rise, go back to the past to look at sea level adaptations to climate changes under similar boundary conditions to the present.
The Littorina transgression: A best analogue to the present sea-level rise Warming climate (the mid- Holocene thermal maximum) Soar of greenhouse gases (e.g. CO 2, CH 4 ) level Absence of major continent ice sheets The Littorina transgression ( cal. BP) is a manifestation of Baltic Sea level rise in response to the pronounced drawdown of global ice volume Littorina littorea Linné
The Littorina transgression - hypotheses and causes Several minor transgression waves (the Danish-Swedish view) Caused by changing global ice volume and regional climate conditions One main transgression (the Finnish view) Caused by the uniform eustatic rise of global sea level
Climate changed, so did Baltic Sea level Evidence from both ice cores and deep-sea sediments reveal that the North Atlantic area has experienced millennial-scale climate changes. Beach ridge, Olsäng (Mikaelsson, 1978)
Beach ridges, Inlängan island (Photo: Berglund, 1964)
Beach ridges on Inlängan and Aspö islands (Berglund, 1964)
Isolation lakes and lagoons: excellent benchmarks of past sea level Dating the isolation/conta ct of the basins may provide a powerful constraint on relative sea- level changes
Smygen lagoon (Photo: Berglund, 2000)
Smygen: -1 m Hunnemara: 3 m Ryssjön: 4.5 m Färsksjön: 7.2 m (the highest lake containing brackish sediments in Blekinge)
Fieldwork (Photo: Berglund, 2000)
Flowchart of lab analyses
First order sea-level changes: Eustasy vs. isostasy A big thaw of the Antarctic Ice Sheet 1st story
Coastal basins: Precise sea-level index points
The Littorina transgression is caused by a continuous ice-volume- equivalent sea-level rise, interspersed with variable rates A changing ice volume?
Storegga tsunami (Andrén, 2001)? Slow down of crustal rebound? Laurentide floods (Tooley, 1989)? A global meltwater pulse 8000 years ago Rapid depletion of seawater 18 O A IRD spike in the South Atlantic (Hodell et al., 2001) Flooding in Chesapeake Bay/8000 cal. BP (Bratton et al., 2003) A break of coral growth in the Caribbean area (Blanchon and Shaw, 1995) Black Sea transgression Global climate during the Noahs Flood
Linking Baltic Sea-level fluctuations to North Atlantic storminess at millennial time scale Coastal dune, W Denmark (Photo: Yu, 2003) 2nd story
Dating sea-level- sensitive floras (e.g. dinoflagellates, diatoms, seagrasses, stoneworts) provides evidence for millennial-scale sea-level changes
Centennial-scale sea-level changes: A window to the NAO past? 3rd story
Sea-level changes: Cycle, cycle all the time? Wavelet and power spectral transforms of a macrofossil series from Lake Ryssjön The 480-yr cycle: tidal origin? 480*2=960 yr 480*3=1440 yr the enigmatic 1500 yr cycle was solved!
Conclusions Within the Littorina Sea phase, five minor transgressions are recorded: L1 8500–8200, L2 7800–6900, L3 6400–5600, L4 5300–4700, and L5 4500– 4100 cal. BP. These minor transgressions, lasting 500–1000 years in the study sites, occurred almost synchronously across the southern Baltic Sea. The Littorina transgression in southeastern Sweden covers the time span 8500–3000 cal. BP. It can be ascribed to the accelerated rise of global sea level, overprinting the slow isostatic uplift in southern Scandinavia during the middle Holocene. The first transgression (L1) can be linked to the flood of the proglacial lakes in North America. The most pronounced transgression (L2) is marked by a Baltic Sea level rise by ca. 8 m in 500 years, at an accelerated rate of ~15 mm yr -1. It suggests a global meltwater pulse probably triggered by the partial collapse of the Antarctic Ice Sheet.
The younger minor transgressions were possibly caused by ice-volume changes in combination with submillennial-scale variations in regional storminess. Centennial-scale sea-level fluctuations show good coherence with ice-core sea-salt ions and cosmogenic nuclides in some time windows, suggesting solar forcing probably through a system similar to the dipole oscillation of the North Atlantic atmosphere (i.e. NAO). In addition, tidal actions related to lunar cycles may exert another important influence on Baltic Sea level during the middle Holocene.