Late Holocene Environmental Changes Research Articles

Late-Holocene and Little Ice Age palaeoenvironmental change inferred from pollen analysis, Isla de los Estados, Argentina

We present pollen and spore analysis from a peat-bog section from southwestern Isla de los Estados (Staaten Island), Tierra del Fuego to better understand late-Holocene environmental change in southernmost Patagonia. The island's position as the easternmost landmass at the southernmost of South America, places it squarely within the influence of the southern westerly winds (SWW) and the Antarctic Circumpolar Current, and so makes the island a unique location to document the palaeoecological response to climate change during the late Quaternary. We compare our Nothofagus pollen record from Bahía Franklin with other Nothofagus pollen records from Isla de los Estados and Tierra del Fuego. Nothofagus has been shown to respond to changes in mean annual temperature in the southern latitudes under cooler climate with little seasonality in precipitation. We also evaluate the correspondence between these changes in vegetation to other late-Holocene environmental proxies that include variations in sea surface temperature (SST) from the Beagle Channel and records of past glacier fluctuations. Our results show that low concentrations of Nothofagus pollen existed at Bahía Franklin at about 4000 cal yr BP. Climate ameliorated between ca. 3500 and 500 cal yr BP based on an increase in frequency and concentration values of Nothofagus and Drimys winteri. Between about 500 and 50 cal yr BP, the pollen record revealed a noticeable decline in the forest density. We interpret the decline in forest density in Isla de los Estados between 500 and ∼50 yr cal BP as a response to cold and windy conditions during the Little Ice Age (LIA). Our interpretation from our Nothofagus pollen record broadly agrees with regional cooling recorded in reconstructed SST of the Beagle Channel and with glacier expansion in the Fuegian Cordillera.

Cryogenic processes and fire activity in a high Atlantic mountain area in NW Iberia (Picos de Europa) during the Mid–Late Holocene

Mid–Late Holocene environmental changes in the Cantabrian Mountains are a consequence of both climate variability and human activity. A 182cm-long sedimentary sequence was collected from Belbín depression, Western Massif of Picos de Europa (Cantabrian Mountains, NW Spain), in order to reconstruct Holocene environmental dynamics and the factors triggering landscape changes in the area. Using multi-proxy analysis of the uppermost 60cm of the sediments (texture, organic matter content, quartz grains microstructures, charcoal deposition) together with three 14C AMS dates, a sequence of alternating warmer and colder phases has been inferred for the last ca. 6.7kycalBP. Warm stages are defined by low to moderate chemical weathering of the quartz grain particles with relative increases of the C/N ratio, while colder phases show a moderate to intense physical weathering of the quartz grains and lower C/N ratios. Warmer temperatures were recorded in Belbín area between: 6.7–5, 3.7–3, 2.6–1.1, 0.87–0.51 and since 0.01kycalBP. A colder regime occurred between 5–3.7, 3–2.6, 1.1–0.87 and 0.51 to 0.01kycalBP. The increasing organic matter content during the Late Holocene may be associated with increasing temperatures. The charcoal particles do not show a higher or lower concentration during prevailing colder or warmer conditions, and therefore may be linked to human-induced fire management of the landscape. The most intense period with fire activity occurred between 3.5 and 3kycalBP during the Bronze Age.

Fluvial response to Late Pleistocene and Holocene environmental change in a Thames chalkland headwater: the Lambourn of southern England

This paper describes the Late Pleistocene to Holocene stratigraphy of the River Lambourn; a minor headwater of the River Thames in the Berkshire Downs. The Quaternary valley-fill comprises around 5–8m of Late Pleistocene gravels overlain by Holocene peats and chalky clays. Quaternary deposits overlie an irregular rockhead erosion surface with deep scouring particularly evident on prominent bends in the valley. The gravels subdivide into a lower unit of chalky gravels overlain by coarse flint gravels. Ground penetrating radar suggests that gravels at depth are relatively structureless, but at the top show well-developed point-bar accretion surfaces which occur in association with peat-filled sinuous channels. These probably date from around the Pleistocene-Holocene boundary and may have formed in response to climate change and increased groundwater outflow as stream hydrology changed from the short-duration, high-magnitude flows of the Lower Dryas to the uniform, low-magnitude flows of the Holocene. Holocene peats initially infilled abandoned floodplain channels at around 10kyr BP but later encroached over much of the Lambourn floodplain. A progressive upward decrease in organic material and an increase in the proportion of chalky clays from around 4kyr BP probably occurred in response to floodplain accretion coupled with increased erosion of the chalk catchment related to agricultural clearance and a wetter climate.

Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan

Late Holocene environmental changes in Lake Hamana, a coastal lagoon in central Japan, were reconstructed by a diatom fossil analysis and tephra and radiocarbon dating of a lakebed sediment core (HMN08-7) with high temporal resolution. On the basis of major species composition changes in diatom assemblages, we divided the core into six zones (I to VI), and subdivided zones V and VI into 3 subzones. The environment of Lake Hamana developed in six stages that corresponded to the diatom zones: stage I (4700–4600 cal BP) was characterized by vigorous seawater inflow in an inner bay environment; during stage II (4600–4500 cal BP), a closed inner bay environment with laminated sediments formed as a result of the formation of sand barriers; stage III (4500–2650 cal BP) was characterized by a well-mixed brackish water environment caused by active mixing with riverine fresh water and, after 3500 cal BP, an enhanced inflow of seawater; during stage IV (2650–2250 cal BP), the salinity of the lake water gradually decreased owing to reduced seawater inflow; during stage V (2250 cal BP to 480 cal BP), the lake water changed from brackish to fresh, although salinity increased temporarily during the middle of the period, and the depth of the lake increased; and during Stage VI (480 cal BP to the present), an inner bay environment developed again following the AD 1498 Meio earthquake, although salinity increased temporarily from AD 1600–1750. We also identified two event deposits, EA and EB, on the basis of spikes in the abundance of minor diatom species. In EA layer (4600–4500 cal BP), Glyphodesmis williamsonii, a marine or brackish water species, was temporarily dominant, and lamination disappeared; therefore, this layer was interpreted to represent a brief episode of sediment supply from seaward, such as by a tsunami or storm surge. The EB layer (ca. 4200 cal BP), in contrast, was characterized by an increase in fresh and fresh to brackish water species, suggesting a temporary supply of allotopic riverine or lake shore sediments during a large flood event.

Late Holocene environmental change in arctic western Siberia

The Putorana Plateau, western Siberia, situated on the boundary of the Atlantic and continental Siberian climate provinces, is sensitive to shifts in atmospheric circulation. Three lakes on an altitudinal transect were studied using chironomid subfossils to provide the first estimates of late Holocene climate in this remote, poorly studied region of Arctic Russia. The analysis of sediment cores from three closely located lakes is rare in palaeoenvironmental studies and enables the role of other environmental variables, which may be a potential source of error in palaeoclimatic reconstructions, to be assessed. The chironomid-based reconstructions suggest a more maritime climate c. 3400 cal. BP with July temperatures c. 1.5°C warmer than present which cooled rapidly by c. 2°C, with a more continental climate between 3200 and 2600 cal. BP. These trends are similar in timing and scale to other northern hemisphere records. The recent chironomid records from all three lakes show pronounced faunal changes over the last 50 years probably directly or indirectly because of climate-driven changes in catchment hydrology. This is particularly evident in the recent record from an open lake within a large wetland habitat, which appears relatively insensitive to changes in July air temperatures.

Historical evolution and Middle to Late Holocene environmental changes in Lake Shkodra (Albania): New evidences from micropaleontological analysis

The 7.5m long SK13 sediment core, drilled at Lake Shkodra (Albania) at a bottom depth of 7m in the central southern part of the lake, was selected for multidisciplinary analysis. The sediment core age spans from 4560calyrBP to present. The origin and the evolution of the lake are still debated and were never investigated in detail. In historical records, until the 15th century Lake Shkodra was never mentioned as such, but as a marshland or as a confluence between two rivers. Our research aims to reconstruct the past biodiversity and the Middle-Late Holocene palaeoenvironmental and palaeoclimatic changes using Ostracods, Characeae, and comparing the micropaleontological data with pollens and stable isotope curves. Thirteen ostracod and five charophyte species were identified. Amongst the ostracods Candona montenigrina and Limnocythere scutariense are endemic of the lake; Candona meridionalis, Paralimnocythere georgevitschi, Metacypris cordata, Candona ex gr. bimucronata, and Cyclocypris sp. have been collected for the first time in Lake Shkodra; the last three taxa occurred only in the lower portion of the sediment core. Amongst the charophytes, Lychnothamnus barbatus and Nitella hyalina are recorded for the first time in the lake and occurs with high frequency throughout the lower portion of the core. A drastic change occurs between 1274 and 1197calyrBP, when 8 ostracod species out of 13 and all charophytes disappear, and the frequency of the remaining 5 species dramatically increases. The micropaleontological data suggest a decrease of the lake biodiversity since around 1200calyrBP linked to the transition between an ancient marshland to a lacustrine environment. This drastic event seems to be independent from any global or local climate change but linked to the complex hydrographic setting of the lake and of its only outlet, the River Bojana, discharging in the Adriatic Sea.

Process implications of chenier dates in Australia

Chenier plains record changes in the mode of coastal progradation between periods of mudflat progradation and coarse sediment deposition. There are several environmental forces responsible for these changes, and these include both intrinsic and extrinsic processes. In Australia, the causes of these changes are still not well understood. The majority of Australian chenier plain studies have been conducted within a relatively narrow spatial scope, focussing on one or two individual plains. Compiling and assessing times of chenier ridge building across multiple sites can provide a broader-scale perspective on chenier plain development trends, potentially revealing broader scale morphodynamic relationships that may exist across a large region. One such assessment was undertaken by Lees and Clements (1987), and since then many more chenier ridge ages have been obtained. Our understanding of late Holocene environmental changes and computation methods have since improved. A new statistical assessment of Australian chenier ridge ages revealed periods of simultaneous chenier ridge building across multiple northern and southern Australian coastal plains between 2400 and 1300 yr BP, and possibly again in the last 1000 years. Previously such results were explained in terms of Holocene climate changes, however the spatial separation between sites in this new assessment suggests that other broad-scale extrinsic processes may provide a better explanation. A possible candidate for such a process is late Holocene sea level changes. • We conducted a statistical analysis of chenier ridge ages from 23 Australian sites. • Our results indicate that ridge formation was not affected solely by local events. • A common phase of chenier ridge formation occurred from 2400 to 1300 yr BP. • Further widespread ridge formation has occurred in the last 1000 years. • We suggest that sea level changes may have played a role in chenier ridge formation.

Evidence of strong storm events possibly related to the little Ice Age in sediments on the southerncoast of Brazil

Late Holocene environmental changes on the southeastern Brazilian coast were assessed using a high-resolution paleoproductivity proxy record from a sediment core collected at 14m water depth in the Pântano do Sul Inlet. Mollusk shells from the core were AMS dated, and sediment grain size, concentrations of organic carbon and total nitrogen, and δ13C and δ15N values were determined to investigate changes in paleoceanographic and paleoclimatic conditions over the depositional period. Most of the parameters showed strong fluctuations in the depth interval corresponding to the Little Ice Age, between 1560 and 1700AD, that were marked by first an increase and then a decrease of input of terrigenous sediments to the inlet. Proxies also indicate that sedimentary conditions were more stable, before and after this period. The strong sedimentary changes observed in the Pântano do Sul Inlet may be related to climatic changes reported elsewhere in South America during 1550 and 1800AD and to severe storm events associated with the enhanced cold fronts that occurred in the southern littoral region during this period.

Late glacial and Holocene environmental changes inferred from sediments in Lake Myklevatnet, Nordfjord, western Norway

Late Glacial and Holocene environmental changes were reconstructed using physical, chemical and biological proxies in Lake Myklevatnet, Allmenningen, (5o13′17″E, 61o55′13″N) located at the northern side of Nordfjorden at the coast of western Norway. Myklevatnet (123 m a.s.l.) lies above the Late Glacial marine limit and contains sediments back to approximately 14,300 years before a.d. 2000 (b2k). Because the lake is located ~48 km beyond the margin of the Younger Dryas (YD) fjord and valley glaciers further inland, and did not receive glacier meltwater from local glaciers during the YD, the lake record provides supplementary information to Lake Krakenes that received glacial meltwater from a local YD glacier. Lake Myklevatnet has a small catchment and is sensitive to Late Glacial and Holocene climate and environmental changes in the coastal region of western Norway. The age-depth relationship was inferred from a radiocarbon- and tephra-based smoothing-spline model with correlated ages from oxygen isotope maxima and minima in the Late Glacial sequence of the NGRIP ice core (in years b2k) to refine the basal chronology in the Myklevatnet record. The results indicate a two-step YD warming, colder early YD temperatures than in the later part of the YD, and considerably more climate and environmental variability during the late Holocene in western Norway than recorded previously in the oxygen isotopes from Greenland ice cores. The Myklevatnet record is also compared with other Late Glacial and Holocene terrestrial and marine proxy reconstructions in the North Atlantic realm.

The Duxbury Sunken Forest—Constraints for Local, Late Holocene Environmental Changes Resulting from Marine Transgression, Duxbury Bay, Eastern Massachusetts, U.S.A.

Gontz, A.M.; Maio, C.V., and Rueda, L., 2013. The Duxbury sunken forest—constraints for local, late Holocene environmental changes resulting from marine transgression, Duxbury Bay, Eastern Massachusetts, U.S.A.The present marine transgression has forced geological and ecological zones vertically higher and landward since the late Pleistocene. A recent investigation in Duxbury Bay, Massachusetts, identified 18 Juniperus virginiana tree stumps emergent on an intertidal flat immediately seaward of a small marsh and pond situated between two eroding drumlins. The position of each stump was mapped with global positioning system (GPS), and its elevation with respect to mean lower low water was surveyed. Samples were selected from four stumps with elevations ranging from 2.03 and 0.75 m above mean lower low water for radiocarbon dating. The samples returned calibrated ages between 2219 ± 94 and 2867 ± 79 cal YBP, with the topographically highest sample returning the youngest date. Stump positions suggest a landscape gradient of 1.4 mm/yr between 2000 and 3000 cal YBP. The results are comparable with high-resolution studies of sea level in eastern Massachusetts for the same time period. Comparison of the youngest paleostumps with modern living trees suggests a dramatic change in the landscape gradient, an increase to 1.8 mm/yr. While this is contrary to sea-level studies nearby, it may represent an increase in the energetics of Duxbury Bay and resultant coastal erosion as the bay floods. The site can be used to put the impacts of changing sea-level rates into a landscape evolution framework.

Late Holocene sedimentation and hydrologic development in a shallow coastal sinkhole on Great Abaco Island, The Bahamas

It remains poorly understood how sea level drives environmental change and hydrographic development in coastal karst basins (underwater caves, sinkholes, blueholes, etc.) over millennial timescales. It was previously hypothesized that coastal karst basins (CKBs) transition from vadose, to littoral, then anchialine, and finally submarine environments as sea-level rise inundates coastal karst landscapes, but the initial flooding event of CKBs remains challenging to sample. Runway Sinkhole hosts a modern anchialine ecosystem located ∼225 m from Great Abaco Island coastline in The Bahamas, and its shallow water depth (∼1.8 mbsl) permits an investigation into the early environmental evolution and hydrographic development in a CKBs after inundation by sea-level rise. Four sediment cores were collected from Runway Sinkhole, and late Holocene environmental change was reconstructed with benthic foraminiferal paleoecology, organic matter geochemistry (OM%, δ13Corg, and C:N), X-radiography, and radiocarbon dating. Despite some uncertainties associated with the chronology, it appears that Holocene sea-level rise initially flooded Runway Sinkhole and created a littoral environment at least by ∼3.9 ka, whereafter a detrital peat deposit accumulated in the sinkhole. This detrital peat had a high organic matter content (mean 88%), a δ13Corg value indicative of organic matter derived from C3 plants including mangroves (−28‰), and an unknown calcareous microfossil suggestive of a non-marine habitat in the sinkhole. A shift to carbonate sand deposition, organic matter with more marine-influenced δ13Corg values (−23‰), and expansion of euryhaline (Bolivina striatula, Elphidium poeyanum, and Triloculina bermudezi) and anchialine (Physalidia simplex and Conicospirillina exleyi) benthic foraminifera at ∼1.2 ka marks the onset of modern anchialine environmental conditions at the sediment–water interface (∼1.8 mbsl). These results suggest that relative sea-level rise in the Bahamas forced environmental change in Runway sinkhole at ∼1.2 ka, and indicate that peat deposits in coastal sinkholes must be verified as in-situ before being utilized as sea-level indicators.

A 3400 year paleolimnological record of prehispanic human–environment interactions in the Holmul region of the southern Maya lowlands

The timing, magnitude and drivers of late Holocene environmental change in the Holmul region of the southern Maya lowlands are examined by combining paleoenvironmental and archeological data. Environmental proxy analyses on a ~3350calyr lacustrine sediment record include pollen, charcoal, loss on ignition, magnetic susceptibility, and elemental geochemistry. Archeological evidence is derived from extensive settlement surveys conducted near the study site. Results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950calyr BP. The fire history shows a dramatic increase in burning during the Classic period, possibly reflecting changing agricultural strategies. A distinct band of carbonate deposited from 1270 to 1040calyr BP suggests decreased hydrologic input associated with drier conditions. Abrupt changes in proxy data around 940calyr BP indicate a cessation of human disturbance and local abandonment of the area.

Mud and magnetism: records of late Pleistocene and Holocene environmental change recorded by magnetic measurements

The paper presents a personal summary of the role of magnetic measurements in lake sediment studies. Examples are used to illustrate the main variations in lake sediment magnetic properties and the processes controlling their variations. These are considered in terms of sediment sequences: (1) that are virtually devoid of magnetic minerals; (2) the magnetic properties of which are dominated by input of magnetic minerals from ‘primary’, unweathered catchment sources (3) with magnetic properties indicative of erosion of weathered material, mainly magnetically enhanced topsoil; (4) that have received minimal input of terrigenous ferrimagnetic minerals but are rich in biogenic magnetite (5) parts of which have experienced dissolution diagenesis (6) in which signals from erosion, biogenic magnetite and dissolution can all be detected and (7) that are dominated by the presence of authigenic greigite. Additional issues, including the importance of particle size variations as a control of magnetic properties, the under-representation of haematite and goethite in the magnetic record and the significance of atmospheric deposition are also considered. A concluding section briefly outlines the present status of environmental magnetism and its role in palaeoenvironmental research based on lake sediment studies.

Late Glacial and Holocene environmental change reconstructed from floodplain and aeolian sediments near Burdukovo, lower Selenga River Valley (Lake Baikal region), Siberia

Floodplain and aeolian sediments near Burdukovo reveal a detailed record of Holocene environmental change in the lower Selenga River Valley (Lake Baikal region, Siberia). During the late Pleistocene and early Holocene fine-grained alluvium accumulated on the floodplain followed by a period of increased landform stability and subsequent pedogenic formation. This part of the stratigraphical sequence yielded rich assemblages of terrestrial molluscs, which increase in species diversity from early pioneer communities with about ten taxa to levels containing over twice that number. The land snail assemblages also record an episode of relatively drier local habitats prior to ∼9.2 ka BP with subsequent wetter conditions lasting until ∼8.0 ka BP. This was followed by an abrupt and sustained change in floodplain deposition, shifting from overbank alluvium to aeolian sedimentation, within which a series of weakly developed soil horizons formed during the middle and late Holocene periods. The onset of aeolian processes and relatively drier conditions in the middle Holocene at Burdukovo coincides with major changes observed both in other regional palaeoenvironmental proxy records and in local archaeological sequences, although it is still not clear how the two are linked.

Late Holocene environmental change in the Albertine Rift: new multi-proxy sedimentary evidence from the Virunga Volcanoes

Late Holocene environmental change in the Albertine Rift: new multi-proxy sedimentary evidence from the Virunga Volcanoes

Late Holocene environmental changes based on diatom and pollen records from lake sediments of Laguna Encantada, in the Neotropical Gran Sabana (Venezuelan Guayana)

Late Holocene environmental changes based on diatom and pollen records from lake sediments of Laguna Encantada, in the Neotropical Gran Sabana (Venezuelan Guayana)

Late Pleistocene and early Holocene climate and environmental changes in the Horton Plains, central Sri Lanka

Late Pleistocene and early Holocene climate and environmental changes in the Horton Plains, central Sri Lanka

Late Holocene natural hazards and environmental change in southern Iran

Late Holocene natural hazards and environmental change in southern Iran

Late Pleistocene and Holocene environmental changes from lake sediments in Larsemann Hills, East Antarctica

Late Pleistocene and Holocene environmental changes from lake sediments in Larsemann Hills, East Antarctica

A multi-proxy record of late Holocene environmental change from lacustrine sediments: Lake Colenso, North Island, New Zealand

A multi-proxy record of late Holocene environmental change from lacustrine sediments: Lake Colenso, North Island, New Zealand