Assessing the use of mangrove pollen as a quantitative sea‐level indicator on Mahé, Seychelles

We investigated the potential of mangrove pollen from Mahé, Seychelles, to improve existing metre‐scale Late Holocene sediment‐based sea‐level reconstructions. Mangrove species at two mangrove sites are broadly zoned according to elevation within the tidal frame. Modern pollen rain from traps deployed for 1 year generally have a poor relationship with modern vegetation, and relatively low pollen production rates. Pollen from mangrove species that live in narrow elevation zones (e.g. Avicennia marina) are poorly represented in modern pollen rain, while pollen from mangrove species that live across a larger elevational range (e.g. Rhizophora mucronata) are relatively well represented. Pollen was found in extremely low concentrations in mangrove surface and core sediments, which inhibited further study into pollen transport and preservation. The results from this modern study demonstrate that utilizing mangrove pollen would not decrease existing metre‐scale vertical uncertainties in Late Holocene sea‐level reconstructions in the Seychelles. We suggest that this approach may still be successful in other locations if mangrove vegetation is (i) zoned at a more extensive lateral scale and (ii) is closely associated with modern pollen rain and surface sediments, and (iii) sedimentological conditions promote the preservation of pollen in fossil sequences

Using relative sea-level data to constrain the deglacial and Holocene history of southern Greenland

This paper presents new Holocene relative sea-level (RSL) data collected from isolation basins close to the town of Paamiut in south west Greenland. The data shows a rapid fall from a marine limit of c. 52 m asl at c. 10.9 cal. ka BP to close to present by c. 9.5 cal. ka BP, at rates of up to c. 32 mm/yr, falling below present for the majority of the Holocene before rising to present in the last 2000 years. The elevation of the RSL lowstand is not well constrained, but was at least below −3 m. This pattern of rapid RSL fall during the early Holocene matches the pattern seen at other southern Greenland locations suggesting rapid, largely simultaneous ice retreat from the area surrounding the Qassimiut Lobe at the start of the Holocene, occurring c. 2000 years after the initial deglaciation of the extreme southern tip of Greenland. The RSL histories from this and other southern Greenland locations are distinct to those recorded further north along the west coast, and are in broad agreement with a pattern of vertical land motion and RSL predicted by the Huy2 model (Simpson et al., 2009), which predicts an 80 m drop in the contribution of vertical land motion to RSL at 10 cal. ka BP between Sisimiut and Paamiut on the west coast. Despite this broad-scale spatial agreement between the RSL data and the Huy2 model, it fails to satisfactorily predict the Holocene RSL histories at Paamiut and other southern Greenland locations. Sensitivity tests indicate that the data-model misfits are most likely due to an over-estimate of the forcing during the Holocene Thermal Maximum (or the response to this forcing) in southern Greenland and error in the North American ice sheets component of the background deglaciation model. Our new data suggests that much of the southern part of the ice sheet acted differently to the area further north. However RSL changes at Paamiut are also largely impacted by regional and larger-scale processes including a bulls-eye of uplift centred on the west, the impact of the Holocene Thermal Maximum and the influence of the collapse of the North American ice sheets

Modelling the effects of sediment compaction on salt marsh reconstructions of recent sea-level rise

This paper quantifies the potential influence of sediment compaction on the magnitude of nineteenth and twentieth century sea-level rise, as reconstructed from salt marsh sediments. We firstly develop a database of the physical and compression properties of low energy intertidal and salt marsh sediments. Key compression parameters are controlled by organic content (loss on ignition), though compressibility is modulated by local-scale processes, notably the potential for desiccation of sediments. Using this database and standard geotechnical theory, we use a numerical modelling approach to generate and subsequently ‘decompact’ a range of idealised intertidal stratigraphies. We find that compression can significantly contribute to reconstructed accelerations in recent sea level, notably in transgressive stratigraphies. The magnitude of this effect can be sufficient to add between 0.1 and 0.4 mm yr−1 of local sea-level rise, depending on the thickness of the stratigraphic column. In contrast, records from shallow (<0.5 m) uniform-lithology stratigraphies, or shallow near-surface salt marsh deposits in regressive successions, experience negligible compaction. Spatial variations in compression could be interpreted as ‘sea-level fingerprints’ that might, in turn, be wrongly attributed to oceanic or cryospheric processes. However, consideration of existing sea-level records suggests that this is not the case and that compaction cannot be invoked as the sole cause of recent accelerations in sea level inferred from salt marsh sediments

Missing sea level rise in southeastern Greenland during and since the Little Ice Age

The Greenland Ice Sheet has been losing mass at an accelerating rate over the past 2 decades. Understanding ice mass and glacier changes during the preceding several hundred years prior to geodetic measurements is more difficult because evidence of past ice extent in many places was later overridden. Salt marshes provide the only continuous records of relative sea level (RSL) from close to the Greenland Ice Sheet that span the period of time during and since the Little Ice Age (LIA) and can be used to reconstruct ice mass gain and loss over recent centuries. Salt marsh sediments collected at the mouth of Dronning Marie Dal, close to the Greenland Ice Sheet margin in southeastern Greenland, record RSL changes over the past ca. 300 years through changing sediment and diatom stratigraphy. These RSL changes record a combination of processes that are dominated by local and regional changes in Greenland Ice Sheet mass balance during this critical period that spans the maximum of the LIA and 20th-century warming. In the early part of the record (1725–1762 CE) the rate of RSL rise is higher than reconstructed from the closest isolation basin at Timmiarmiut, but between 1762 and 1880 CE the RSL rate is within the error range of the rate of RSL change recorded in the isolation basin. RSL begins to slowly fall around 1880 CE, with a total amount of RSL fall of 0.09±0.1 m in the last 140 years. Modelled RSL, which takes into account contributions from post-LIA Greenland Ice Sheet glacio-isostatic adjustment (GIA), ongoing deglacial GIA, the global non-ice sheet glacial melt fingerprint, contributions from thermosteric effects, the Antarctic mass loss sea level fingerprint and terrestrial water storage, overpredicts the amount of RSL fall since the end of the LIA by at least 0.5 m. The GIA signal caused by post-LIA Greenland Ice Sheet mass loss is by far the largest contributor to this modelled RSL, and error in its calculation has a large impact on RSL predictions at Dronning Marie Dal. We cannot reconcile the modelled RSL and the salt marsh observations, even when moving the termination of the LIA to 1700 CE and reducing the post-LIA Greenland mass loss signal by 30 %, and a “budget residual” of + ~ 3 mm yr−1 since the end of the LIA remains unexplained. This new RSL record backs up other studies that suggest that there are significant regional differences in the timing and magnitude of the response of the Greenland Ice Sheet to the climate shift from the LIA into the 20th century

Global extent and drivers of mammal population declines in protected areas under illegal hunting pressure

Illegal hunting is a persistent problem in many protected areas, but an overview of the extent of this problem and its impact on wildlife is lacking. We reviewed 40 years (1980–2020) of global research to examine the spatial distribution of research and socio-ecological factors influencing population decline within protected areas under illegal hunting pressure. From 81 papers reporting 988 species/site combinations, 294 mammal species were reported to have been illegally hunted from 155 protected areas across 48 countries. Research in illegal hunting has increased substantially during the review period and showed biases towards strictly protected areas and the African continent. Population declines were most frequent in countries with a low human development index, particularly in strict protected areas and for species with a body mass over 100 kg. Our results provide evidence that illegal hunting is most likely to cause declines of large-bodied species in protected areas of resource-poor countries regardless of protected area conservation status. Given the growing pressures of illegal hunting, increased investments in people’s development and additional conservation efforts such as improving anti-poaching strategies and conservation resources in terms of improving funding and personnel directed at this problem are a growing priority

Testing models of mid to late Holocene sea-level change, North Queensland, Australia

Understanding the nature of global ice-equivalent eustatic sea-level changes during the mid to late Holocene is important to our understanding of how ice sheets will respond to future climate change. This study re-analyses the indicative meaning and age control of existing relative sea-level (RSL) data from Cleveland Bay, North Queensland, Australia and presents new RSL data from a foraminifera-based transfer function as a preliminary test of global geophysical models in this region during the mid to late Holocene. The foraminifera-based transfer function produces reliable RSL estimates, consistent through the mid to late Holocene at different locations in Cleveland Bay. Analysis of the combined RSL database reveals that RSL rose above present between 8 and 6.2 ka cal. BP, with the peak of the sea-level highstand c. 2.8 m above present at c. 5 ka cal. BP, remaining relatively stable above +1.5 m from 6.2 until at least 2.3 ka cal. BP, falling to present in the last millennia. This long period of sea level above present in the mid to late Holocene suggests a gradual rather than abrupt end to global ice melt, which must have continued into the late Holocene. This new analysis also shows no evidence for episodic fluctuations within the highstand, although they cannot be entirely ruled out by this study. This study demonstrates that more sea-level data needs to be collected from locations uncontaminated by glacio-isostasy, hydro-isostasy and tectonic effects, in order to better constrain the late Holocene melt histories of the large polar ice sheets