Dinoflagellate cyst and pollen assemblages as tracers for marine productivity and river input in the northern Gulf of Mexico

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Abstract

Both marine dinoflagellate cysts and terrestrially derived pollen and spores are abundant in coastal
sediments close to river mouths, making sediment records from such settings ideal to simultaneously study land–
ocean climate interactions, marine productivity patterns and freshwater input over time. However, few studies
consider the combined calibration of these palynological proxies in modern coastal sediments offshore from
rivers, which is needed to strengthen the interpretation of paleoreconstructions. Here, we analyze the palynological content of marine surface sediments along land–sea transects off the Mississippi and Atchafalaya river
mouths in the northern Gulf of Mexico (GoM) and test three palynological indices which are often employed
in the paleo-domain: (i) the abundance of cysts of heterotrophic and autotrophic dinoflagellates (dinocysts) as a
tracer for primary productivity (H /A ratio) and (ii) the ratio between non-bisaccate pollen and bisaccates (P /B)
as well as (iii) the ratio between pollen (excluding bisaccates) and dinocysts (P /D), which are both tracers for
river input and distance to the coast.
Our results show that dinoflagellate cysts are most abundant on the shelf, where heterotrophic dinocyst species
dominate coastal assemblages in reach of the river plume, while autotrophic taxa are more present in the oligotrophic open ocean. This is clearly reflected in decreasing H/A values further offshore. Individual dinocyst taxa
also seem to inhabit specific niches along an onshore–offshore transect, linked to nutrient availability and proximity to the turbid river plume. The highest pollen concentrations are found close to the Mississippi river mouth
and mostly represent a mixture of local coastal and upstream vegetation, whereas bisaccate pollen was most
abundant further offshore of the Mississippi river. Multivariate redundancy analysis (RDA) performed on both
pollen and dinocyst assemblages, a set of environmental parameters, and the three palynological ratios showed
that net primary productivity was the most important variable influencing the dinocyst assemblages, likely as
the result of nutrient input. Additionally, the RDA confirmed that the H/A ratio indeed seems to track primary
productivity, while the P /B ratio results in a robust indicator for distance to the coast, and the P /D ratio better
reflects river input. Together, our data confirm and further specify the suitability of these three palynological
ratios in river-dominated coastal margins as proxies for (past) marine productivity and distance to the coast and
river.
Original languageEnglish
Pages (from-to)257-276
Number of pages20
JournalJournal of Micropalaeontology
Volume42
Issue number2
DOIs
Publication statusPublished - 27 Nov 2023

Bibliographical note

Publisher Copyright:
© 2023 Copernicus GmbH. All rights reserved.

Funding

This research has been supported by the Netherlands Earth System Science Centre (grant no. 024.002.001).

FundersFunder number
Netherlands Earth System Science Centre024.002.001

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