Mathematics – Logic
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..os42a01b&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #OS42A-01
Mathematics
Logic
1600 Global Change (New Category), 3309 Climatology (1620), 3322 Land/Atmosphere Interactions, 3344 Paleoclimatology, 4215 Climate And Interannual Variability (3309)
Scientific paper
The Little Ice Age (LIA) was a late Holocene interval of climate cooling registered in the North Atlantic region by expansion of alpine glaciers and sea ice. Here the LIA includes an early phase from about AD 1280 to AD 1390, along with a main phase from about AD 1550 to AD 1860, followed by warming and ice retreat. It has recently been demonstrated from records of North Atlantic ice-rafted debris that the LIA is the latest cooling episode in a pervasive 1500 yr cycle of the climate system that may lie at the heart of abrupt climate change. This raises the question of whether the LIA climate signal is globally synchronous (implying atmospheric transfer of the climate signal) or out of phase between the polar hemispheres (implying ocean transfer of the climate signal by a bipolar seesaw of thermohaline circulation). New Zealand is ideally situated to address the problem as it is located on the opposite side of the planet from the classic North Atlantic region where the classic LIA signal is so clearly registered. Due to high precipitation and ablative activity gradients, glaciers in the Southern Alps of New Zealand respond to climate change on a decadal timescale. Therefore, moraine sequences deposited during oscillations of these glaciers are ideal for determining the character of the LIA signal in this portion of the Southern Hemisphere. The chronology of the well-developed late Holocene moraines fronting the Hooker and Mueller Glaciers in the Southern Alps is controversial. Initial dating of these moraines from historical records, as well and from lichenometric and tree-ring analyses pointed to a LIA climate signal in the Southern Alps, indicating a globally synchronous event. However, a subsequent chronology based on weathering rinds of surface clasts suggested that most of the late Holocene moraines antedate the LIA, implying the lack of a classic LIA climate signal in this portion of the Southern Hemisphere. To resolve this dilemma, a detailed chronology of the Hooker and Mueller Holocene moraine systems was constructed in this study by using geomorphologic maps, historical records, and the FALL lichenometry technique. A major result of this study is that most of the Holocene moraines fronting the Mueller and Hooker Glaciers were deposited during the main phase of the LIA as defined in the North Atlantic region. The glacier advances recorded by these moraines are about equivalent in age with those in the North Atlantic region. The magnitude and timing of the LIA climate signal is the same in the two regions. The collapse of the Hooker and Mueller Glaciers in the last 140 yrs is also approximately synchronous with that of glaciers in the North Atlantic region. Therefore, the LIA climate signal occurs in the atmosphere as far south as New Zealand, on the other side of the planet from the North Atlantic region.
Black J. L.
Halteman B. A.
Maasch Kirk A.
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