Abstract. The modern-day Godavari River transports large amounts of
sediment (170 Tg per year) and terrestrial organic carbon
(OCterr; 1.5 Tg per year) from peninsular India to the
Bay of Bengal. The flux and nature of OCterr is considered
to have varied in response to past climate and human forcing. In order to
delineate the provenance and nature of organic matter (OM) exported by the
fluvial system and establish links to sedimentary records accumulating on its
adjacent continental margin, the stable and radiogenic isotopic composition
of bulk OC, abundance and distribution of long-chain fatty acids (LCFAs),
sedimentological properties (e.g. grain size, mineral surface area, etc.) of
fluvial (riverbed and riverbank) sediments and soils from the Godavari basin
were analysed and these characteristics were compared to those of a sediment
core retrieved from the continental slope depocenter. Results show that river
sediments from the upper catchment exhibit higher total organic carbon (TOC)
contents than those from the lower part of the basin. The general
relationship between TOC and sedimentological parameters (i.e. mineral
surface area and grain size) of the sediments suggests that sediment
mineralogy, largely driven by provenance, plays an important role in the
stabilization of OM during transport along the river axis, and in
the preservation of OM exported by the Godavari to the Bay of Bengal. The stable
carbon isotopic (δ13C) characteristics of river sediments
and soils indicate that the upper mainstream and its tributaries drain
catchments exhibiting more 13C enriched carbon than the lower
stream, resulting from the regional vegetation gradient and/or net balance
between the upper (C4-dominated plants) and lower
(C3-dominated plants) catchments. The radiocarbon contents of
organic carbon (Δ14COC) in deep soils and eroding
riverbanks suggests these are likely sources of “old” or pre-aged carbon to
the Godavari River that increasingly dominates the late Holocene portion of
the offshore sedimentary record. While changes in water flow and sediment
transport resulting from recent dam construction have drastically impacted
the flux, loci, and composition of OC exported from the modern Godavari
basin, complicating reconciliation of modern-day river basin geochemistry
with that recorded in continental margin sediments, such investigations
provide important insights into climatic and anthropogenic controls on OC
cycling and burial.
Robust simulation of mineral precipitation–dissolution problems with variable mineral surface area
