Rare earth element distribution in the NE Atlantic: Evidence for the
temporal and spatial stability of the seawater signature and the
influence of benthic sources
Abstract
Seawater rare earth element (REE) concentrations are increasingly
applied to reconstruct water mass histories by exploiting relative
changes in the distinctive normalised patterns. However, the mechanisms
by which water masses gain their REE patterns are yet to be fully
explained. To examine this, we collected water samples along the
Extended Ellett Line (EEL), an oceanographic transect between Iceland
and Scotland, and measured dissolved REE by offline automated
chromatography (SeaFAST) and ICP-MS. The proximity to two continental
boundaries, the incipient spring bloom coincident with the timing of the
cruise, and the importance of deep water circulation in this
climatically sensitive gateway region make it an ideal location to
investigate sources of REE to seawater and the effects of vertical
cycling and lateral advection on their distribution. The deep waters
have REE concentrations closest to typical North Atlantic seawater and
are dominated by lateral advection. Comparison to published seawater REE
concentrations of the same water masses in other locations provides a
first measure of the temporal and spatial stability of the seawater REE
signature. We demonstrate the REE pattern is replicated for
Iceland-Scotland Overflow Water (ISOW) in the Iceland Basin from
adjacent stations sampled 16 years previously. A recently published
Labrador Sea Water dissolved REE signature is reproduced in the Rockall
Trough but shows greater light and mid REE alteration in the Iceland
Basin, possibly due to the dominant effect of ISOW and/or continental
inputs. An obvious concentration gradient from seafloor sediments to the
overlying water column in the Rockall Trough, but not the Iceland Basin,
highlights release of light and mid REE from resuspended sediments and
pore waters, possibly a seasonal effect associated with the timing of
the spring bloom in each basin. This study highlights the need for fully
constrained REE sources and sinks, including the temporary nature of
some sources, to achieve a balanced budget of seawater REE. In this
contribution, I discuss some of the potential mechanisms and their
implications for the longevity of the seawater REE signature.