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Coastal vegetation evidence for sea level changes associated with Heinrich Events

PAGES News • Vol.17 • No 2 • June 2009
Science Highlights: Paleo Sea Level
Figure 2: A) A sedimentary sequence including a paleosol (fossil soil) that caps the Pleistocene substrate, basal
peat and lagoonal mud from the Mississippi Delta. Note the sharp contact (arrow) between the ~2 cm thick peat
layer and the overlying lagoonal mud, which represents an abrupt sea level rise at ca. 8.2 cal ka BP. B) Stratigraphic
signature of the abrupt sea level rise at ca. 8.2 cal ka BP at Bayou Sale, Mississippi Delta (Törnqvist et al., 2004). The
occurrence of Rangia cuneata, a brackish water clam characteristic of estuarine and lagoonal environments, is
also shown.
Coastal vegetation evidence for sea level changes
associated with Heinrich Events
Ca T a l i n a Go n z á l e z a n d ly d i e M. du p o n T
MARUM - Centre for Marine Environmental Sciences, Geosciences Department, University of Bremen, Germany;
A Cariaco Basin pollen record shows the development of tropical salt marshes during marine isotope stage
3 and suggests that millennial sea level changes during the periods encompassing Heinrich Events followed
Antarctic climate variability.
The timing of sea level changes during
marine isotope stage 3 (MIS 3; 60-25 ka)
is a key issue in understanding the role
of ice sheets in millennial-scale climate
variability. The available reconstructions
of sea level changes during this interval
greatly rely on oxygen isotope records
from deep-sea cores (since coral-based
data are sparse and chronologies less pre-
cise), and consistently show four cycles of
similar amplitude of sea level change in
the order of 20-30 m (Siddall et al., 2008
and references therein). However, there
is little agreement on the exact timing of
these changes or on the relative roles of
the Southern and Northern Hemisphere
ice sheets in global sea level scenarios.
The ecological response of sensitive
terrestrial ecosystems can provide inde-
pendent information that complements
the almost exclusively marine body of
evidence of millennial sea level change.
For this purpose, intertidal tropical eco-
systems can be particularly useful, since
they are very sensitive to environmental
gradients in the sea-continent interface.
In tidal salt marsh plant communities,
species composition varies with eleva-
tion, usually in a banded pattern parallel
to the shore. Its variation often reects
environmental gradients that result from
the interaction between tidal regime, local
topography, freshwater input, and biota. It
has been proposed that the zonation is a
spatial expression of successional changes
over time and has potential to be recon-
structed for the past by pollen analysis. If
patterns of pollen deposition follow zona-
tion and succession patterns, these can be
Barber et al., 1999). This rapid sea level rise
serves as an example of how the amount
and source of meltwater can be inferred
from sea level records by the ngerprint-
ing method; a technique that capital-
izes on the distinct spatial pattern of the
global sea surface due to the gravitational
attraction of large ice and/or water masses
(Mitrovica et al., 2001; Clark et al., 2002;
Kendall et al., 2008). However, more de-
tailed records are required to rene the es-
timate of the water volume impounded in
these glacial lakes. To this end, our ongo-
ing high-resolution sea level work in the
Mississippi Delta aims to rene the timing
and amplitude of the rapid sea level rise
corresponding to the “8.2 ka event” by de-
tailed stratigraphic studies. With regard to
the “7.6 ka event”, its extent still remains a
matter of debate. Some records suggest a
ca. 3 m rapid rise that occurred at about
7.5 cal ka BP or slightly later (e.g., Siddall et
al., 2003; Liu et al., 2004; Bird et al., 2007),
while others indicate a smooth rise of sea
level during this time window (e.g., Van de
Plassche, 1982; Törnqvist et al., 2006). The
causes of such spatial contrasts are at pres-
ent unknown but may in part be related to
the location of the associated meltwater
sources and their sea level ngerprints.
We therefore conclude that our under-
standing of rapid sea level rise during the
early Holocene is still in its infancy. Many
more high-resolution sea level records for
this critical time interval are needed. Com-
bined with “ngerprint modeling”, they
could serve to rene the timing, amplitude
and origin of such abrupt events.
Carlson, A.E., Legrande, A.N., Oppo, D.W., Came, R.E., Schmidt, G.A.,
Anslow, F.S., Licciardi, J.M. and Obbink, E.A., 2008: Rapid early
Holocene deglaciation of the Laurentide ice sheet, Nature Geosci-
ence, 1: 620-624.
Kendall, R.A., Mitrovica, J.X., Milne, G.A., Törnqvist, T.E. and Li, Y., 2008:
The sea level fingerprint of the 8.2 ka climate event, Geology, 36:
Törnqvist, T.E., Bick, S.J., Gonzalez, J.L., van der Borg, K. and de Jong,
A.F.M., 2004: Tracking the sea level signature of the 8.2 ka cool-
ing event: New constraints from the Mississippi Delta, Geophysi-
cal Research Letters, 31: L23309.
Törnqvist, T.E., Bick, S.J., van der Borg, K. and de Jong, A.F.M., 2006: How
stable is the Mississippi Delta? Geology, 34: 697-700.
Yu, S.-Y., Berglund, B.E., Sandgren, P. and Lambeck, K., 2007: Evidence for
a rapid sea level rise 7600 yr ago, Geology, 35: 891-894.
For full references please consult:
PAGES NewsVol.17 • No 2 • June 2009
Science Highlights: Paleo Sea Level
Figure 1: Left - main ecological preferences of 3 salt marsh taxa. R ight - schematic representation of salt marsh
community dynamics in a changing sea level environment according to the Cariaco Basin pollen record (González
and Dupont, 2009). Thicker black lines indicate areas of soil hypersalinity. SL 1 to SL4 denote different sea levels
reconstructed from the pollen record and correspond with phases indicated in Fig. 2. a) Establishment of salt
marshes when arid conditions promote extensive hypersaline environments; b) rapid sea level rise causes erosion;
only pioneer species tolerate the change; c) sea level rise decelerates, and accretion of sediments and autochthonous
organic material takes place; more competitive species take advantage of favorable conditions; d) sea level drops,
sediment accumulation constrains the tidal influence to the seaward edge.
reconstructed back in time by establishing
a time-depth relationship with the fossil
evidence, this then enables past sea level
to be reconstructed. Here, we present new
palynological evidence from the marine
core MD03-2622 collected from the Ca-
riaco Basin that reconstructs the history
of intertidal plant communities during
intervals associated with Heinrich Events
(HEs), linking them to the well-constrained
North Atlantic signal of millennial- to sub-
The Cariaco Basin is located on the
northern shelf of Venezuela and is particu-
larly sensitive to the seasonal shifts of the
Intertropical Convergence Zone (ITCZ),
which deeply inuence the hydrology and
oceanographic features of the basin. Dur-
ing MIS 3, the Cariaco Basin record displays
a clear North Atlantic climatic variability,
shifting from dry conditions during cold
stadials to wet conditions and increased
river runo during warm interstadials. This
hydrological pattern is reected by varia-
tions in the input of terrestrial materials
and has been explained by the latitudinal
migration of the ITCZ (Peterson et al., 2000;
Peterson and Haug, 2006; González et al.,
2008). The chronology used in this study
was established by linking similar features
of sediment reectance prole of Cariaco
site MD03-2622 with that of the nearby
ODP Site 1002D, which has an extremely
high-resolution age model for the past 60
ka (Hughen et al., 2004; 2006).
Tropical salt marsh response to
millennial climate and sea level
During glacial periods, when sea level was
80-120 m lower than today, a broad shal-
low shelf became exposed south of the
Cariaco Basin. Periods of extremely dry
atmospheric conditions might, therefore,
have resulted in hypersaline coastal en-
vironments (Medina et al., 1989). These
extreme conditions could have been tol-
erated only by a limited number of plant
species. Chenopodiaceae, Poaceae and
Cyperaceae belong to the most common
representatives of salt tolerant plants in
tropical and subtropical wetlands (Adam,
2002) (Fig. 1).
The pollen record
Five high-amplitude vegetation shifts were
recorded in the pollen record during MIS
3 (60-25 ka), indicating rapid oscillations
of environmental conditions in north-
ernmost South America. Recurrent salt-
tolerant vegetation expansions (i.e., the
development of salt marshes) were shown
to correlate with HEs 3-6. Within single HE
intervals, a recurrent and directional suc-
cession of pollen taxa was observed in
the following order: Abrupt increases in
saltbush (Chenopodiaceae) followed by a
dominance of grasses (Poaceae), which in
turn were replaced by sedge (Cyperaceae)
(Fig. 2). Once interstadial conditions re-
turned, salt marshes were replaced by
mangroves and other arboreal species.
In this sequence, salt marshes started
to develop under extremely arid stadial
conditions (Peterson and Haug, 2006;
González et al., 2008) when intertidal habi-
tats became hypersaline due to extended
periods of strong evaporation and reduced
rainfall. The salt marshes were most likely
restricted to narrow intertidal areas be-
cause under strongly seasonal conditions
they are usually fringed on the landward
side by extensive bare salt pans (Fig. 1a, b;
Adam, 2002). Early colonizing species of
salt marshes, like the annual Atriplex and
Salicornia (Chenopodiaceae), rst colonize
bare zones of lower and middle marsh ar-
eas, with a high incidence of waves and
prolonged inundation regimes (Ranwell,
1972). Thus, intervals of maximum pol-
len representation of Chenopodiaceae
are interpreted as periods of direct tidal
inuence and sediment relocation. Fre-
quent tidal ooding under accelerated sea
level rise would result in ooding of the
marsh surface, transforming it into a new
seaoor, with the later landward accretion
of new, low marsh sediments (Fig. 1b).
By comparing our high-resolution
pollen data with sea level reconstructions
from the Red Sea (Arz et al., 2007; Siddall
et al., 2008 and references therein) and
the independently dated fossil corals from
the Huon Peninsula (Thompson and Gold-
stein, 2006) for the period between 40.5-38
ka, we found that the phase dominated by
Chenopodiaceae corresponds closely with
an interval of accelerated sea level rise (Fig.
2). This conrms that only early succes-
sional plants, with high colonizing abilities
(e.g., rapid growth, annuals or short-lived
perennials) were capable of surviving the
stressful high rates of change (Fig. 1a).
Moreover, the erosion of low marsh sedi-
ments would wash out and transport the
pollen produced in situ (Fig. 1b).
As soon as sea level rise decelerated
(ca. 1 ka after the Chenopodiaceae peak),
some vegetation was able to establish per-
manently. In low marsh areas, sediment
accretion greatly depends on vegetation
cover, which limits erosion, and enhances
sediment and organic matter trapping.
Thus, areas covered with vegetation ex-
perienced higher marsh heights. The
PAGES News • Vol.17 • No 2 • June 2009
Science Highlights: Paleo Sea Level
Figure 2: Comparison of the high-resolution palynological record from core MD03-2622 (Cariaco Basin) with sea
level reconstructions from Red Sea marine sediment cores and Huon Peninsula (Papua New Guinea) fossil corals
during HE 4 (González and Dupont, 2009). Top to bottom: Reflectance data from core MD03-2622 (Laj, 2004). Sea
level data; dark blue line - central Red Sea (Siddall et al., 2003; 2008), light blue line - northern Red Sea (Arz et
al., 2007), and dotted pink line - Huon Peninsula (Thompson and Goldstein, 2006). Pollen % of Chenopodiaceae,
Poaceae, and Cyperaceae indicating the directional alternation of salt marsh species during HE4. Dotted gray
lines SL1 to SL4 denote different sea levels reconstructed from the Cariaco Basin pollen record, which correspond
to phases explained in Figure 1.
build-up of middle and high marsh envi-
ronments favored the expansion of more
competitive perennial grasses (Poaceae),
thus replacing Chenopodiaceae pioneer
species (Figs. 1c, d and 2). In contrast, the
presence of Cyperaceae indicates less sa-
line conditions, since sedges do not toler-
ate salinity excess. Thus, since there is no
evidence of increased freshwater input
during HEs, Cyperaceae pollen maxima
might reect an expansion of elevated
marsh areas (Fig. 1c, d).
Once interstadial conditions resumed
and the average position of the ITCZ
shifted northwards, the increased avail-
ability of freshwater might have alleviated
salinity stress on soils, allowing a more
complex plant community to develop on
the shelf, and pushing the upper borders
of the salt marsh seawards. Simultaneous
increases in mangrove pollen (González
and Dupont, 2009) conrm that coastal
environments became less saline and in-
creasingly suitable for the establishment
of forests during stadial-interstadial tran-
sitions. In addition to freshening, deceler-
ated sea level rise (or sea level fall) would
be required to allow the establishment of
mangroves, since mangroves do not sur-
vive if sea level rise occurs too rapidly (El-
lison, 1993; Woodroe, 1999).
The Cariaco Basin pollen record also shows
a similar relation between salt-marsh ex-
pansion and sea level rise during HEs 3, 5,
5a and 6, in spite of dating uncertainties
and poorer resolution of the vegetation
data (González and Dupont, 2009). In all
ve cycles, maximum values of Chenopo-
diaceae pollen coincide with the onset of
HE stadials in the North Atlantic, and with
warming phases in Antarctica. According
to our palynological evidence, sea level
started to rise before the ice sheet collapse
that caused Heinrich layers in the North
Atlantic, being in agreement with both
Red Sea sea level reconstructions during
the HE 4 (Fig. 2; Siddall et al., 2008; Arz et
al., 2007) and with fossil coral data from
the Huon Peninsula (Thompson and Gold-
stein, 2006). However, a subsequent decel-
erated rise or fall of sea level is needed to
reconcile with the expansion of Poaceae.
In this case, our data supports the timing
of central Red Sea reconstruction (Siddall
et al., 2003; 2008; Rohling et al., 2008),
the independently dated corals from the
Huon Peninsula, and models, which sug-
gest that melting in Antarctica might have
accounted for a rise in sea level of about
20 m (Rohling et al., 2004; 2008; Flückiger
et al., 2006).
Through the palynological reconstruction
of intertidal vegetation in core MD03-2622
we provided indirect evidence of rapid sea
level change during MIS 3. Five intervals
of expanded salt marsh vegetation corre-
sponded to the onset of HEs of the north-
ern high latitudes and suggest periods of
accelerated sea level rise in the tropical
Atlantic. The close relationship between
sea level rise and community dynamics is
consistent with a resource-based mecha-
nism of succession, where soil develop-
ment and salinity gradients are the main
factors determining the vegetation dy-
namics of coastal marshes. In this context,
the Cariaco Basin palynological record is
especially informative on the timing of sea
level changes during MIS 3 and their con-
nection with HEs, supporting the idea that
sea level uctuations followed Antarctica
climate variability.
This work was supported by the Programme
Alβan –the European Union Programme of High
Level Scholarships for Latin America (Scholar-
ship E04D047330CO) and the Deutsche Aka-
demische Austausch Dienst (DAAD)-Colfuturo
Program. Data will be available in PANGAEA
Adam, P., 2002: Saltmarshes in a time of change, Environmental Conser-
vation, 29: 39-61.
Arz, H.W., Lamy, F., Ganopolski, A., Nowaczyk, N. and Pätzold, J., 2007:
Dominant Northern Hemisphere climate control over millennial-
scale glacial sea-level variability, Quaternary Science Reviews,
26: 312–321.
González, C. and Dupont, L.M., 2009: Tropical salt marsh succession as
sea-level indicator during Heinrich events, Quaternary Science
Reviews, 28: doi: 10.1016/j.quascirev.2008.12.023.
Siddall, M., Rohling E.J., Thompson, W.G. and Waelbroeck, C., 2008:
Marine isotope stage 3 sea level fluctuations: Data synthesis
and new outlook, Reviews of Geophysics, 46: RG4003, doi:
Thompson, W.G. and Goldstein, S.L., 2006: A radiometric calibration of
the SPECMAP timescale, Quaternary Science Reviews, 25: 3207-
For full references please consult:
... In such cases, the pollen of marsh vegetation is a good indicator of environmental variability (e.g. González and Dupont 2009). In fact, pollen of Amaranthaceae, Cyperaceae and Poaceae has been used to reconstruct past sea-level fluctuation (Hodell et al., 1991;Higuera-Gundy et al., 1999;González and Dupont, 2009). ...
... González and Dupont 2009). In fact, pollen of Amaranthaceae, Cyperaceae and Poaceae has been used to reconstruct past sea-level fluctuation (Hodell et al., 1991;Higuera-Gundy et al., 1999;González and Dupont, 2009). Other taxa such as Batis maritima, Sesuvium portulacastrum, and herbaceous Asteraceae and Fabaceae taxa are abundant along beaches, and their pollen in sedimentary sequences usually indicates environmental stages prior to mangrove establishment (e.g. ...
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RESUMEN Se realizó una revisión de los efectos del incremento en el nivel del mar, los cambios en la salinidad y las per-turbaciones humanas sobre la dinámica de los mangla-res. Los efectos de estos factores se analizaron a escalas seculares en seis registros palinológicos tomados en el Caribe Colombiano. A pesar del incremento acelerado en el nivel del mar, los incrementos en las temperaturas del mar y del aire y las disminuciones en la precipitación en los dos últimos siglos, los manglares han aumentado su representación en los registros de palinológicos en varios sitios de la región, ubicados tanto en el continente como en las islas oceánicas. Tal expansión de los manglares se asocia con su capacidad de mantener el substrato con-trarrestando el incremento en el nivel mar con el aumento en las cargas de sedimentos aluviales, desde 1850 AD en los sitios continentales, y con el aumento en la acu-mulación de turba autóctona en los suelos de la isla de San Andrés. Las pérdidas de manglares en el pasado, se asociaron a la erosión costera, y/o al efecto combinado del incremento regional en las sequías y en la salinidad. Estos procesos han ocasionado la muerte de los man-glares o cambios en la composición de especies. Cuando se incrementan la salinidad del substrato y la deposición de arenas, pasan de ser manglares dominados por Rhi-zophora mangle a los dominados por Avicennia germi-nans. La capacidad de rebrote de los tallos dañados de Avicennia germinans parece ser el rasgo que le ha per-mitido a esta especie expandirse después de la ocurrencia de sequías intensas y prolongadas y de vientos fuertes, tormentas tropicales y huracanes. Las perturbaciones humanas se representaron por la expansión de Lagun-cularia racemosa y Avicennia germinans a expensas de Rhizophora mangle, o por el reemplazo de la vegetación arbórea por vegetación herbácea (pastizales o cultivos) y especialmente dominada por el helecho Acrostichum aureum. Alrededor de 1850 AD, los manglares y al ve-getación de playa fueron reemplazados por plantaciones de coco en la isla de San Andrés y en la bahía de Cis-patá las áreas pantanosas fueron cubierta con cultivos de arroz. Aunque después de 1900 AD se abandonaron estos cultivos debido a una incursión marina, ha pre-valecido la dominancia de Laguncularia racemosa en los registros de polen indicando la intervención humana permanente desde entonces Palabras clave: Cambio climático, sa-linidad, deforestación, sequía, nivel del mar. ABSTRACT We review the main effects of sea level rise, salinity changes, and human disturbances on mangrove forest dynamics. The effects of these drivers on mangrove communities are evaluated at centennial time scales in the light of six palynological records from the Colombian Caribbean. Despite the accelerated rates of sea level rise, increases in sea surface and air temperatures, and decreases in precipitation of the last two centuries, mangroves have shown an increasing representation in pollen records at continental and marine locations of the region. In continental settings, such expansions have been related to the offsetting of sea levels by the increasing loads of fluvial sediments since 1850 AD, and by increases in autoch-thonous peat accumulation in San Andrés Island. Losses of mangrove cover in the past have been related to coastal erosion, regional droughts, and salinity increases. Such processes have commonly caused mangrove die-off or changes in forest species composition. When the substrate has become more saline, or sand sedimentation has increased significantly, the composition of mangrove communities has switched towards the dominance of Avicennia germinans at expenses of Rhizophora mangle. Re-sprout capacity of damaged stems of Avicennia germinans seems to have been the trait that has allowed this species to increase after strong and prolonged droughts, and occurrence of strong winds, tropical storms, and hurricanes. Human disturbances are represented either by the expansion of Laguncularia racemosa and Avicennia germinans and decreases of Rhizophora mangle, or by mangrove replacement by herba-ceous vegetation (grasses or crops), especially the fern Acrostichum aureum. Around 1850 AD, mangroves and beach vegetation were replaced by coconut plantations in San Andrés Island, and in the Cispatá bay swampy areas were covered with rice crops. Although after 1900 AD these crops were abandoned because of a marine incursion, Laguncularia racemosa has prevailed so far indicating pervasive anthropogen-ic disturbances.
... For example, mangrove pollen assemblages in tropical regions can accurately indicate the nearshore location of ancient coastal lines [39], and the pollen content variation of Pinus and some certain herbs can indicate changes in the shoreline and sea level [43]. The changes in the number of Quinoa, grasses and Cyperaceous flowers were used by some researchers to reconstruct the sea-land transition of the Cariaco Basin borehole in South America since the MIS3 stage, and the H event was accurately retrieved at once [44,45]. ...
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According to previous studies, the Lixiahe area in the east of the Jianghuai River was an alternate environment of land and sea in the middle Holocene, and it was not until the late Holocene that the eastern Jianghuai completely became a terrestrial environment. However, recent archaeological studies have found that the extensive Neolithic sites in the Lixiahe area have recorded the rich human activities and cultural connotations of the prehistoric civilization in the Middle Holocene. In this paper, the Gangxi section of Jianhu Lake, Jiangsu Province (GX2) was selected and pollen analysis was fulfilled, then the geomorphic evolution process of the study area from sea to land was investigated according to the palynological assemblages and algae fossils of brackish water, semi-saline water, fresh water and terrestrial in the section strata. During the period of 8500–3800 cal. BP, GX2 was affected by multiple factors such as sea surface fluctuation, ocean flow and sediment deposition carried by seagoing rivers. Since 5800 cal. BP, the area east of the Grand Canal between the Yangtze River and the Huaihe River, and the west of the Yangzhai town, Funing–Longgang town, Yancheng–Dagang town and Yancheng–west of the Dongtai–Hai’an line, have become a terrestrial environment. After the eastern Jianghuai became a land, the Liangzhu culture (5300–4300 cal. BP) in the Taihu Lake basin in the south wing of the Yangtze River delta expanded to the eastern Jianghuai area, and the Longshan culture and Yueshi culture in the Haidai area in the north also migrated south to the eastern Jianghuai area. Admittedly, the main reason in the process of Neolithic cultural development is the internal motivation that the ancient ancestors struggled with nature and pushed forward the continuous development of civilizations. However, our study explains the palaeogeographical origin of Neolithic culture in the eastern and coastal areas of Jianghuai in the middle Holocene, and meanwhile, provides an example for the man–land relationship research on Neolithic culture.
... This variability is to be expected for M.I.S. 3, (60-25 ka), as M.I.S. 3 was a period considered to have been highly unstable, climatologically, with conditions not existing (non-analog) in present-day environments. There seem to have been repeated decadal -scale warming events of 8 o -15 o C (Dansgaard-Oeschger (D-O) Events) during this stage (Stewart, 2005;Siddall, et al, 2008) With Gonzalez and Dupont (2009) reporting as many as five high-amplitude vegetation shifts during the stage. The timing of excursions, in the pine-oak ratio, likewise, suggest possible correlations with Heinrich events (HE 2-4) date (Hemmings, 2004;Watts et al. 1992;Grimm, et al, 2006). ...
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The use of palynofacies as a conceptual tool for the study of depositional environments augments and extends the pointsource studies using geophysical, lithological correlation and microfossil analyses of sediment cores in the offshore. We present a synthesis of palynofacies research in the South Atlantic Bight/Georgia Bight, USA. Two research localities - Gray's Reef National Marine Sanctuary (GRNMS) and nearby J-Reef - on the same (-20 m) isobath and only 16 km distant form one another, were characterized in our study. Vibracores to over 4 m below the sea floor were taken at both locations together with hand cores. Outcrops and seafloor exposures were hand sampled. These data are varied and, synthesized elsewhere, yielded insights into the Quaternary paleoenvironments of the coastal plain. Nearshore marine, barrier-back barrier, estuarine- marsh and upland biota provide geologic and ecologic proxies in the form of micro and macrobotanical remains - to include pollen, spores, diatoms, foraminifera and wood. The use of several techniques, notably optical stimulated luminescence (OSL), accelerator mass spectroscopic-radiocarbon (AMS-RC), amino acid racemization (AAR), and uranium series dating methods) has produced a presumptive chronostratigraphy that extends from the Holocene to oxygen isotope stage (M.I.S.) 5. Models based on our pollen results are compared to others proposed for the Mid-Atlantic and Southeast Atlantic regions of the Atlantic coastal plain. Analyses-sedimentological, geophysical, paleoecological and chronological-in the area of Gray's Reef National Marine Sanctuary (GRNMS), have increased our understanding of the late Pleistocene paleoecology and that of relative sea level (RSL) for the now drowned Atlantic Coastal Plain. Palynological data provide a clearer picture of the ecology of the Atlantic Coastal Plain in the latter Pleistocene Epoch, M.I.S.5 through and post-Last Glacial Maximum (LGM/M.I.S.2/Holocene). Arboreal species, notably oak and pine, dominate the pollen spectra and show clear climate-related variability most notably with Heinrich Events.
... The ECSS was covered by forest-steppe during late MIS 3 according to the characteristics of modern pollen assemblages from forest-steppe area in Inner Mongolia, Ningxia and Shaanxi province . Cyperaceae cannot tolerate saline conditions, but favor a stable wetland (González and Dupont, 2009). At present, a sedge and reed community is widely distributed around wetland of the Yangtze River estuary and Taihu Lake (Tang and Lu, 2003;Tian et al., 2008). ...
... The ECSS was covered by forest-steppe during late MIS 3 according to the characteristics of modern pollen assemblages from forest-steppe area in Inner Mongolia, Ningxia and Shaanxi province . Cyperaceae cannot tolerate saline conditions, but favor a stable wetland (González and Dupont, 2009). At present, a sedge and reed community is widely distributed around wetland of the Yangtze River estuary and Taihu Lake (Tang and Lu, 2003;Tian et al., 2008). ...
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A high-resolution pollen record derived from DG9603 core reveals vegetation and climate changes on the East China Sea Shelf (ECSS) during the past 30 000 years. From 29.8 to 26.6 cal ka BP, the ECSS was covered by warm temperate forest-steppe and wetland, indicating a relatively temperate and moist environment. During the period of 26.6–14.8 cal ka BP (including the Last Glacial Maximum), wetland and temperate forest-steppe developed around the ECSS. From 14.8 to 5.3 cal ka BP, sea-level continuously rose, and the ECSS was gradually submerged. In some exposed areas of the ECSS and lower reaches of the Yangtze River, northern subtropical forest (with plants of Quercus-evergreen, Castanopsis–Lithocarpus and Tsuga) developed instead of temperate forest-steppe and wetland. The pollen record shows that the rainfall and temperature increased continually during the period of 14.8–12.8 cal ka BP. At the end of this period, subtropical forest expanded and even reached the level of “Holocene Optimum period” (early-mid Holocene). IN the Younger Dryas period (12.8–11.1 cal ka BP), a rapid increase in the proportion of arboreal taxa especially Quercus-deciduous tree, and a slight decrease in Quercus-evergreen, Tsuga and herbs component indicates a mild climate with higher precipitation. From 11.1 to 5.3 cal ka BP, the northern subtropical forest was widely distributed around the ECSS region, suggesting a relative warm and humid condition in the early Holocene. The subtropical forest component declined slightly and herbaceous taxa increased, reflecting a relatively drier and cooler climate during the period of 9.0–7.0 cal ka BP. In the past 5.3 cal ka BP, forest vegetation in the lower reaches of the Yangtze River was deforested severely, possibly caused by human activity.
Mangroves are ecosystems that are seriously threatened by climate change, particularly sea level rise and an increase of droughts. They are resilient to short droughts but their response to longer ones remains arguable. In this work, we studied the responses of R. mangle dominated forests on a carbonate island (El Rosario Island) to climate anomalies and their drivers at inter-annual, decadal and inter-decadal scales during the last centuries. Palynological analysis of a sediment core retrieved from an R. mangle dominated forest was used to reconstruct vegetation changes during the last 400 years. Time series, Multi-taper spectral, Fourier and correlation analyses of PDO, AMO and ENSO series were performed to identify the matches between these series and mangrove changes during this time. The pollen record showed the influence of coastal dynamics on mangrove vegetation changes on a local scale and the influence of climate on a regional one. Changes in coastal vegetation and mangroves were influenced by beach ridge formations and lagoon closing, which were, in turn, determined by shifts in wave and wind intensity. The simultaneous diminution of both types of vegetation were related to both natural (earthquake and extreme droughts) and anthropogenic disturbances. Our results also showed the replacement of the Rhizophora dominated forest by an Avicennia dominated forest when droughts became longer. The peaks of Rhizophora pollen percentages identified along the pollen record showed a 64 year recurrence cycle that dominated during the Little Ice Age (1610–1862) and a 32 year cycle during the Current Warm Period (1866–1954). While the first cycle was positively correlated with the warm phase of PDO and AMO time series, the second cycle showed a negative significant correlation with PDO, AMO and ENSO time series. During warm periods, mangroves were stressed by droughts, but as these cycles became shorter, mangroves could recover more rapidly. From 1954 to the present, no significant correlations were observed between vegetation changes and climate drivers, which is likely related to the increased anthropogenic disturbance beyond that period of time. Our results show the high resilience of mangroves to cyclic climate changes that involve droughts, winds and sea level rises but low recovery and species turnover with extreme and longer droughts and strong anthropogenic disturbances.
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Saltmarshes are a major, widely distributed, intertidal habitat. They are dynamic systems, responding to changing environmental conditions. For centuries, saltmarshes have been subject to modification or destruction because of human activity. In this review, the range of factors influencing the survival of saltmarshes is discussed. Of critical importance are changes in relative sea level and in tidal range. Relative sea level is affected by changes in absolute sea level, changes in land level and the capacity of saltmarshes to accumulate and retain sediment. Many saltmarshes are starved of sediment because of catchment modification and coastal engineering, or exposed to erosive forces, which may be of natural origin or reflect human interference. The geographical distribution of individual saltmarsh species reflects climate, so that global climatic change will be reflected by changes in distribution and abundance of species, although the rate of change in communities dominated by perennial plants is difficult to predict. Humans have the ability to create impacts on saltmarshes at a range of scales from individual sites to globally. Pressures on the environment created by the continued increase in the human population, particularly in developing tropical countries, and the likely consequences of the enhanced greenhouse effect on both temperature and sea level give rise to particular concerns. Given the concentration of population growth and development in the coastal zone, and the potential sensitivity of saltmarsh to change in sea level, it is timely to review the present state of saltmarshes and to assess the likelihood of changes in the near (25 years) future. By 2025, global sea level rise and warming will have impacts on saltmarshes. However, the most extensive changes are likely to be the direct result of human actions at local or regional scales. Despite increasing recognition of the ecological value of saltmarsh, major projects involving loss of saltmarshes but deemed to be in the public interest will be approved. Pressures are likely to be particularly severe in the tropics, where very little is known about saltmarshes. At the local scale the cumulative impacts of activities, which individually have minor effects, may be considerable. Managers of saltmarshes will be faced with difficult choices including questions as to whether traditional uses should be retained, whether invasive alien species or native species increasing in abundance should be controlled, whether planned retreat is an appropriate response to rising relative sea level or whether measures can be taken to reduce erosion. Decisions will need to take into account social and economic as well as ecological concerns.
The astronomical theory of climate change asserts that Earth's climate is affected by changes in its orbit, which vary the seasonal and latitudinal distribution of solar radiation. This theory is the basis of the orbitally tuned SPECMAP timescale. A key constraint for this important chronology was the mid-point of the Penultimate Deglaciation, initially dated to 127,000 years ago. Recent work suggests this event may be considerably older, casting doubt on the astronomical theory, the SPECMAP timescale, and the accuracy of orbitally tuned chronologies. Difficulties with U/Th coral dating of sea-level events have impeded progress on this problem, because most corals are not closed systems. Here, we use a new approach to U/Th dating that corrects for open-system behavior and produces a sea-level curve of sufficient resolution to confidently correlate with SPECMAP over the last 240,000 years, permitting a reassessment of both this critical chronology and a central tenet of climate change theory. High-precision ages for 24 oxygen isotope events provide a 240,000-year chronology for marine delta18O records that is independent of orbital tuning assumptions. Although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the Marine Isotope Stage 7/6 boundary, a comparison of radiometric and SPECMAP ages for identical isotope events suggest that the SPECMAP timescale is quite accurate and that its errors were, in general, overestimated. Despite suborbital complexity, orbital cyclicity is clearly evident in our record. High-amplitude sea-level oscillations at periods greater than ˜20,000 years are very close in phase to summer insolation in the Northern Hemisphere. Although sea-level changes cannot be uniquely tied to a specific season or latitude of insolation forcing, the simplest explanation is that long-period, high-amplitude sea-level change is linked to Northern Hemisphere insolation forcing. These results validate the principles of orbital tuning and suggest such timescales are generally robust.
a b s t r a c t Centennial–millennial dynamics of tropical salt marsh vegetation are documented in the pollen record from marine core MD03-2622, Cariaco Basin, Venezuela, which spans the glacial period between 63 and 29 ka. Five rapid and abrupt expansions of salt marsh vegetation are linked with North Atlantic Heinrich events (HEs). Within each event, a recurrent pattern – starting with species of Chenopodiaceae, followed by grasses, and subsequently by Cyperaceae species – suggests a successional process that is determined by the close relationship between sea-level and community dynamics. The salt tolerant Chenopodiaceae, at the base of each sequence, indicate hypersaline intertidal environments, which were most likely promoted by extremely dry atmospheric conditions. Rapid sea-level rise characterizes the onset of HE stadials, causing erosion of marsh sediments, and continued recruitment of pioneer species (Chenopo-diaceae), which are the only ones capable of tolerating the rapid rate of disturbance. Once, as sea-level drops or as rise decelerates, marsh plants are able to trap and stabilize sediments, favouring the establishment of more competitive species (graminoids). The increment of marsh height as a result of autochthonous sediment accumulation reduces the extent of hypersaline environments, and allows the establishment of mesohaline species. These results add to the scarce knowledge on tropical salt marsh ecosystems, and provide independent paleoclimatic evidence on sea-level changes occurring simulta-neously with Antarctica climate variations.
Based on a radiocarbon and paleomagnetically dated sediment record from the northern Red Sea and the exceptional sensitivity of the regional changes in the oxygen isotope composition of sea water to the sea-level-dependent water exchange with the Indian Ocean, we provide a new global sea-level reconstruction spanning the last glacial period. The sea-level record has been extracted from the temperature-corrected benthic stable oxygen isotopes using coral-based sea-level data as constraints for the sea-level/oxygen isotope relationship. Although, the general features of this millennial-scale sea-level records have strong similarities to the rather symmetric and gradual Southern Hemisphere climate patterns, we observe, in constrast to previous findings, pronounced sea level rises of up to 25 m to generally correspond with Northern Hemisphere warmings as recorded in Greenland ice-core interstadial intervals whereas sea-level lowstands mostly occur during cold phases. Corroborated by CLIMBER-2 model results, the close connection of millennial-scale sea-level changes to Northern Hemisphere temperature variations indicates a primary climatic control on the mass balance of the major Northern Hemisphere ice sheets and does not require a considerable Antarctic contribution.
Marine isotope stage 3 sea level fluctuations: Data synthesis and new outlook
  • M Siddall
  • E J Rohling
  • W G Thompson
  • C Waelbroeck
Siddall, M., Rohling E.J., Thompson, W.G. and Waelbroeck, C., 2008: Marine isotope stage 3 sea level fluctuations: Data synthesis and new outlook, Reviews of Geophysics, 46: RG4003, doi: 10.1029/2007RG00226.