Marine Isotope Stage 6
Generated by GPT-5-miniExpansion Funnel Raw 44 → Dedup 0 → NER 0 → Enqueued 0
| Marine Isotope Stage 6 | |
|---|---|
 | |
| Name | MIS 6 |
| Period | Pleistocene |
| Epoch | Middle Pleistocene |
| Start | ~191 ka |
| End | ~130 ka |
| Named for | Oxygen isotope stages |
| Preceding | Marine Isotope Stage 7 |
| Following | Marine Isotope Stage 5 |
Marine Isotope Stage 6
Marine Isotope Stage 6 was a major glacial interval of the Pleistocene occurring roughly between 191 and 130 thousand years ago. It represents one of the large-amplitude oxygen isotope excursions recorded in deep-sea cores underpinning correlations among Antarctic Ice Sheet, Greenland Ice Sheet and continental records such as speleothems from Sierra Nevada and loess sequences from the Chinese Loess Plateau. MIS 6 is frequently discussed in literature alongside events like the Last Glacial Maximum and interglacial transitions represented by Marine Isotope Stage 5.
Definition and Chronology
The stage is defined by stratigraphic δ18O maxima in benthic foraminifera recovered from North Atlantic and South Atlantic sites, anchored to chronological tie points from Uranium–thorium dating of Coral terraces and isotopic chronologies from Vostok and EPICA ice cores. Age models combine astronomical tuning using the Milankovitch cycles with radiometric constraints from Electron spin resonance and Argon–argon dating on tephra layers. Chronologies differ among marine, ice, and terrestrial records, producing debated onset and termination ages that researchers reconcile through global stratigraphic frameworks like the International Commission on Stratigraphy guidelines.
Global Climate and Oceanography
MIS 6 was characterized by expanded continental ice, lowered global temperatures, and changes in ocean circulation including reorganized Atlantic Meridional Overturning Circulation reconstructed from neodymium and carbon isotope gradients in North Atlantic cores. Sea-surface temperature reconstructions from planktic foraminifera show cooling across the North Atlantic Ocean, Pacific Ocean and Southern Ocean, with poleward shifts in frontal systems such as the Subantarctic Front. Atmospheric greenhouse gas concentrations recorded in EPICA Dome C and Greenland ice cores show reduced CO2 and CH4 relative to interglacials, affecting radiative forcing. Transient modelling studies using climate models including Community Earth System Model and Hadley Centre simulations reproduce large-scale cooling and changes in precipitation patterns over regions like the Sahara and Amazon Basin.
Ice Sheets and Sea Level Changes
The glaciation hosted substantial growth of the Laurentide Ice Sheet, expansion of the Fennoscandian Ice Sheet, and increased ice on the Greenland Ice Sheet and portions of the Antarctic Peninsula. Ice-sheet reconstructions from cosmogenic nuclide dating on erratics and exposure surfaces at sites such as the Canadian Shield and Scandinavian Mountains indicate maximum ice extent and outlet glacier advances. Global mean sea level estimates derived from oxygen isotopes, coral reef terraces on islands like Bahamas and uplifted sequences in Mediterranean Sea margins suggest reductions of 60–120 meters below present, with complex regional signal due to glacial isostatic adjustment modelled using Earth rheology parameters constrained by data from the British Isles and Fennoscandia.
Regional Expressions and Paleoenvironments
In Europe, pollen records from lacustrine deposits in the Loire Valley and peat sequences in the British Isles indicate tundra-steppe ecosystems replacing temperate forests, while periglacial features are documented in the Carpathian Mountains. North American records from the Mississippi River corridor and Great Lakes basins document glacial lobes, proglacial lakes, and ice-marginal kames. Asian continental records, including speleothems from Himalaya caves and loess units on the Chinese Loess Plateau, show aridity in monsoon domains and dust flux increases. Southern Hemisphere sites such as Patagonia and the Transantarctic Mountains display moraine sequences and glacier advances synchronous with northern maxima, indicating near-global glaciation patterns modulated by regional forcing.
Proxy Records and Dating Methods
Key proxies include benthic and planktic δ18O and δ13C from foraminifera, alkenone Uk'37 SST estimates from coccolithophore assemblages, pollen spectra, leaf wax hydrogen isotopes, and ice-core gas isotopes (δD, δ18O, CO2, CH4). Chronological control uses uranium-thorium series dating of corals, optically stimulated luminescence of loess, argon–argon on interbedded tephra, and cosmogenic exposure dating (10Be, 26Al) of glacial deposits. Multiproxy stacking approaches integrate regional stacks like the LR04 stack with ice-core chronologies such as the GICC05 and Antarctic timescales to refine phase relationships among marine, ice, and terrestrial signals.
Causes and Climate Forcing Mechanisms
The primary pacing of MIS 6 reflects orbital forcing driven by variations in eccentricity, obliquity, and precession (the Milankovitch cycles), modulating high-latitude insolation and ice-sheet growth. Feedbacks include ice-albedo amplification, lowered atmospheric CO2 mediated by ocean carbon uptake and biological pump changes, and alterations in Atlantic circulation including possible Heinrich-like events associated with ice-rafted debris in the North Atlantic. Tectonic boundary conditions, volcanic aerosol episodes, and variations in continental configuration contributed secondarily; modelling experiments link these forcings to simulated glacial inception and maintenance consistent with palaeodata from Antarctic Peninsula, Siberia, and Southern Ocean records.