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Review
Long-term retrospection on mangrove development using sediment cores
and pollen analysis: A review
Joanna C. Ellison
Aquatic Botany
Volume 89, Issue 2, Pages 93-104
Abstract
Mangroves are biogenic systems that accumulate sedimentary sequences, where
cores can provide records of mangrove species variation in distribution with past
climate change and sea-level change. Fossil evidence used for palaeoecological
reconstruction is based on organic remains that preserve identifying features so
that they can be identified to generic levels at least. This includes macrofossils such
as fruit, flowers, wood or leaves, or microfossils particularly pollen. Anaerobic
conditions in mangrove sediment allow the long-term preservation of these fossil
records. Fossil pollen from core samples is concentrated for microscopic
examination by use of standard chemical treatments, but refinements of these are
necessary for the peculiarities of mangrove peat. Pollen diagrams are expressed in
concentrations, or more usefully in mangrove environments as proportions
relative to others, as this has been shown to demonstrate the depositional
environment actually underneath the mangrove forest. Radiocarbon dating of
sedimentary sequences is used to date palaeoecological successions shown by
fossil sequences, or long-term sedimentation rates. Sediment accretion in the last
50–200 years can been analysed better using Cs137 and Pb210 analyses. From pollen
and macrofossils mostly recovered from stratigraphic cores of sedimentary rock
and more recent sediment, the evolution and dispersal of mangroves through
geological time has been reconstructed. While reconstruction of actual
temperatures in these earlier records is associative to the fossil types present, it is
apparent that mangroves have always been tropical species, extending to higher
latitudes only during global warm periods. Many sedimentary records show
mangroves deeper than the present lower limit of mangrove growth at mean sealevel. These indicate sea-level rising over time, and mangroves keeping pace with
rising sea-level. Stratigraphic dating shows accretion rates of 1 mm a−1 for low
island locations, and up to 1.5 mm a−1 in high islands/continental margins.
Sedimentary records can also show die-off of mangroves with more rapid sea-level
rise and replacement by open water during rising sea-level, landward retreat of
mangrove zones, or replacement of mangroves by freshwater forest with
sedimentary infill. The causes of mangrove community changes identified in the
palaeoecological record can only be inferred by comparison with ecological studies
in the modern environment, the link between the two that may be possible
through long-term mangrove monitoring being poorly established.
Keywords: Stratigraphy; Pollen analysis; Palaeoecology; Macrofossil;
Sedimentation; Palynolog
PALAIOS; October 2009; v. 24; no. 10; p. 650-656; DOI: 10.2110/palo.2009.p09036r
Late Holocene hydrologic and vegetation changes at Turneffe Atoll, Belize,
compared with records from mainland Central America and Mexico
Matthew J. Wooller*,1,2,5, Hermann Behling3, Juan Leon Guerrero4, Nele Jantz3
and Martin E. Zweigert3
Alaska Stable Isotope Facility, Water Environmental Research Center, University
of Alaska Fairbanks, Fairbanks, Alaska 99775, USA
2 School of Fisheries and Ocean
Sciences, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA
3
Department of Palynology and Climate Dynamics, Albrecht-von-Haller-Institute for
Plant Sciences, University of Göttingen, Untere Karspüle 2, 37073 Göttingen,
Germany
4 Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska
99775, USA
5 ffmjw@uaf.edu
1
We present pollen and stable isotope ( 13C, 18O, 15N) data from a 4 m core
(TNF-1) of primarily mangrove peat taken from Turneffe Atoll, Belize. Radiocarbon
(accelerator mass spectrometry) dates show that the record represents ca. 5000
years of sediment accumulation. Vegetation composition varied between dominant
mangroves (primarily Rhizophora mangle) and Chenopodiaceae-Amaranthaceae,
most likely Salicornia bigelovii. The pollen data, along with inferences from stable
isotope analyses of bulk peat and fossil leaf fragments, indicate that marked
environmental changes occurred at this location over the past ca. 5000 years.
There was a transition between ca. 4100 and 2900 cal yr BP, from vegetation
dominated by relatively tall mangroves (R. mangle) to one dominated by
Chenopodiaceae-Amaranthaceae and then Myrica, most likely wax myrtle (M.
cerifera). These changes bracket a period centered at ca. 3500 calibrated years
before present, where there is a peak in the 18O of mangrove leaf fragments. This
timing corresponds with other paleoenvironmental records of climate drying in
Central America and increases the geographic and habitat scope (i.e., mangrove
habitat) of records documenting these changes. Interpretations of shifts in
mangrove habitat, however, require consideration of additional environmental
influences, including changes in groundwater hydrology and relative inputs of
seawater and freshwater (i.e., precipitation) during the Holocene.