Neoglacial climate anomalies and the Harappan metamorphosis
<p>Climate exerted constraints on the growth and decline of past human societies but our knowledge of temporal and spatial climatic patterns is often too restricted to address causal connections. At a global scale, the inter-hemispheric thermal balance provides an emergent framework for un...
| Main Authors: | , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-11-01
|
| Series: | Climate of the Past |
| Online Access: | https://www.clim-past.net/14/1669/2018/cp-14-1669-2018.pdf |
| Summary: | <p>Climate exerted constraints on the growth and
decline of past human societies but our knowledge of temporal and spatial
climatic patterns is often too restricted to address causal connections. At a
global scale, the inter-hemispheric thermal balance provides an emergent
framework for understanding regional Holocene climate variability. As the
thermal balance adjusted to gradual changes in the seasonality of insolation,
the Intertropical Convergence Zone migrated southward accompanied by a
weakening of the Indian summer monsoon. Superimposed on this trend, anomalies
such as the Little Ice Age point to asymmetric changes in the extratropics of
either hemisphere. Here we present a reconstruction of the Indian winter
monsoon in the Arabian Sea for the last 6000 years based on paleobiological
records in sediments from the continental margin of Pakistan at two levels of
ecological complexity: sedimentary ancient DNA reflecting water column
environmental states and planktonic foraminifers sensitive to winter
conditions. We show that strong winter monsoons between ca. 4500 and
3000 years ago occurred during a period characterized by a series of weak
interhemispheric temperature contrast intervals, which we identify as the
early neoglacial anomalies (ENA). The strong winter monsoons during ENA were
accompanied by changes in wind and precipitation patterns that are
particularly evident across the eastern Northern Hemisphere and tropics. This
coordinated climate reorganization may have helped trigger the metamorphosis
of the urban Harappan civilization into a rural society through a push–pull
migration from summer flood-deficient river valleys to the Himalayan piedmont
plains with augmented winter rains. The decline in the winter monsoon between
3300 and 3000 years ago at the end of ENA could have played a role in the
demise of the rural late Harappans during that time as the first Iron Age
culture established itself on the Ghaggar-Hakra interfluve. Finally, we
speculate that time-transgressive land cover changes due to aridification of
the tropics may have led to a generalized instability of the global climate
during ENA at the transition from the warmer Holocene thermal maximum to the
cooler Neoglacial.</p> |
|---|---|
| ISSN: | 1814-9324 1814-9332 |