OCEAN 320 Lecture Notes - Lecture 5: Climate Sensitivity, Foraminifera, Nitrogen Cycle
Unit 5D
A Tale of Two Oceans
Primary Question: What drove transition from warm Pliocene to cold Pleistocene,
dominated by widespread Northern Hemisphere glaciation?
Transitions between one climate state and another are intervals where a # of proxies tend
to be driven to agreement
oEx: productivity, nutrient and circulation proxies sometimes diverge during
glacial/interglacial states of the Pleistocene ocean, but typically agree strongly
during Termination events between climactic states
oReveals more about connections between circulation, upwelling, and productivity
in ocean in times of turmoil as well as tendency of other factors that allow secular
drift during times of stability
Pliocene Ocean
oAbout 3 degrees C higher than todays ocean, had 30% higher CO2 concnetration
(than preinductrial levels), had a permanent El Nino state with reduction in east-
west pressure gradient which affected wind regimes and heat distribution
oResulted in deepening of thermocline and reduction of upwelling intensities in
Pacific, intensification of thermohaline circulation in North Atlantic, enhanced
heat transportation in Gulf Stream and North Atlantic Current (increasing North
Atlantic temps)
Pleistocene Ocean (3 Ma later)
oClosure of Panama and Indonesia corridors in tropics, affecting deep
thermohaline circulation, reorganized oceanic/atmospheric systems
oReduction in sea-surface temp occur at same time of upwelling in equatorial
pacific and eastern ocean basin coastal regions intensified
oCoastal upwelling caused general aridification of land to eat dur to lowered water
vapor content above cold upwelling zones
oGlacial-interglacial cyclicity linked to buildup and retreat of Northern
Hemisphere ice sheet and variability in atmospheric CO2
oCharacterized by shoaling of thermocline and development of active upwelling
cells in equatorial pacific ocean and eastern ocean basins, provoking increase of
primary productivity and less atmospheric CO2
Impacts of reorganization of ocean circulation in transforming upwelling, biological
productivity, and continental climate
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Pacific, intensification of thermohaline circulation in north atlantic, enhanced heat transportation in gulf stream and north atlantic current (increasing north. Hemisphere ice sheet and variability in atmospheric co2: characterized by shoaling of thermocline and development of active upwelling cells in equatorial pacific ocean and eastern ocean basins, provoking increase of primary productivity and less atmospheric co2. Petm: most dramatic geological confirmation of greenhouse theory that increased co2 in atmosphere warmed earths surface. Large release of organic c-depleted carbon caused global carbon isotopic excursion, widespread deep-ocean acidification, and carbonate dissolution. Carbon was removed over 100,000 years through silicate weathering and precipitation of carbonate in ocean/uptake by biosphere and subsequent burial as organic carbon. Warming associated with carbon release implied ~2 doublings of atmospheric pco2 unless climate sensitivity was significantly different during paleogene. Most organisms did not suffer mass extinction. Geographic distribution of organisms was radically rearranged by warming, tropical forms moved poleward in both marine and terrestrial realms.
