Paleoenvironmental reconstruction in La Paz Bay, Gulf of California: Evidence from δ18O in Chione californiensis

Oceanic characteristics of the Holocene are used to understand climatic patterns and phenomena that affect marine and human communities. Likewise, past marine conditions can be reconstructed from surface sea temperature (SST), using stable oxygen isotopes in bivalve shells. The objective of this study was to calculate Holocene summer SSTs for La Paz Bay, by analyzing δ18O of 14C dated bivalve shells ( Chione californiensis) from a Holocene camp site located in Cañada de La Enfermería, Baja California Sur, México. Aragonite was extracted from the shells’ umbo, representing the summer growth season during the first year of life. δ18O value of C. californiensis is −1.9 ± 0.1‰ at present, and varied between −1.3‰ and −2.6‰ during the last 9 ky. In 9469 BP, 8396 BP, and 7708 BP, δ18O values were similar to those of the present. In 7857 BP, 7805 BP, and 7804 BP, δ18O was 18O depleted (0.6–0.9‰), indicating warmer summer SSTs versus the present. In 7070 BP, 6945 BP, and 2087 BP, δ18O was enriched in 18O (0.3–0.4‰), suggesting colder SSTs versus the present. This study coincides with other paleotemperature studies for the region and allows us to address the effect of changing SST on this marine resource, its use by human communities of the past, and its effects on human presence in the area with respect to climate variability.

A paleolimnological investigation of agricultural intensification, water quality and ecosystem change at Lake Nganoke, southern Wairarapa, NZ

<p>Decreasing water quality of lakes as a result of anthropogenic landuse and specifically agricultural intensification is well documented in New Zealand. However, monitoring records of lake health are typically short, only commencing once signs of lake deterioration are observed. The shortness of the instrumental record precludes a detailed understanding of the relationship between landuse change, lake ecosystem trajectories and the effectiveness of mitigation strategies such as riparian planting. Paleolimnological reconstruction from sediment cores has the potential to develop high-resolution time series that may extend lake monitoring centuries into the past. This thesis uses paleoenvironmental reconstruction to investigate lake ecosystem change and water quality in Lake Nganoke, Wairarapa, New Zealand as a result of landuse intensification. The primary aim of this thesis is to reconstruct the past environment of Lake Nganoke from a pre-human reference state to the current day to assess: 1) how increased nutrient fluxes associated with landuse intensification have impacted the lake ecosystem; and 2) the ability of riparian zones to buffer these fluxes. The reconstruction was achieved using a multi proxy approach with pre and post-human environments of Lake Nganoke characterised using Palynology, geochemistry, eDNA and hyperspectral scanning. Māori land clearance was identified at ~AD 1450 (95% CI: AD 1417-1551). The appearance of Pinus pollen and increases in fertilisation and stocking rates placed European arrival at ~AD 1850 (95% CI: 1809 - 1870), while intensification of agricultural landuse occurred post ~AD 1950 (95% CI: 1948 - 1964). The prehuman environment of Lake Nganoke experienced little change, with the catchment dominated by tall trees and likely heavily forested. The lake ecosystem and water quality during this time showed little to no change, with algal productivity likely driven by a constant input of natural nutrients. Post Māori arrival, algal productivity was reduced suggesting an increase in water quality likely driven by added lake marginal plants providing a riparian buffer to terrestrially derived nutrients. Lake productivity increased dramatically post European arrival ~AD 1850, coeval with an increase in sediment Cd, suggesting that fertilisation may have driven a decline in water quality. Further increases in fertilisation and stocking rates indicate additional agricultural nutrient fluxes entering Lake Nganoke in AD 1950 when agriculture intensified. Abundances in denitrifying Gammaproteobacteria indicate increases in nutrient loading while bloom forming Cyanobacteria peak ~AD 2000 before declining till present. Riparian planting following Māori arrival appears sufficient to buffer the lake against increased terrestrial nutrient fluxes associated with land clearing. However, a riparian zone that covers the majority of the catchment post European settlement was inadequate in altering the lake’s degrading ecosystem and water quality trajectory.</p>

A paleolimnological investigation of agricultural intensification, water quality and ecosystem change at Lake Nganoke, southern Wairarapa, NZ

<p>Decreasing water quality of lakes as a result of anthropogenic landuse and specifically agricultural intensification is well documented in New Zealand. However, monitoring records of lake health are typically short, only commencing once signs of lake deterioration are observed. The shortness of the instrumental record precludes a detailed understanding of the relationship between landuse change, lake ecosystem trajectories and the effectiveness of mitigation strategies such as riparian planting. Paleolimnological reconstruction from sediment cores has the potential to develop high-resolution time series that may extend lake monitoring centuries into the past. This thesis uses paleoenvironmental reconstruction to investigate lake ecosystem change and water quality in Lake Nganoke, Wairarapa, New Zealand as a result of landuse intensification. The primary aim of this thesis is to reconstruct the past environment of Lake Nganoke from a pre-human reference state to the current day to assess: 1) how increased nutrient fluxes associated with landuse intensification have impacted the lake ecosystem; and 2) the ability of riparian zones to buffer these fluxes. The reconstruction was achieved using a multi proxy approach with pre and post-human environments of Lake Nganoke characterised using Palynology, geochemistry, eDNA and hyperspectral scanning. Māori land clearance was identified at ~AD 1450 (95% CI: AD 1417-1551). The appearance of Pinus pollen and increases in fertilisation and stocking rates placed European arrival at ~AD 1850 (95% CI: 1809 - 1870), while intensification of agricultural landuse occurred post ~AD 1950 (95% CI: 1948 - 1964). The prehuman environment of Lake Nganoke experienced little change, with the catchment dominated by tall trees and likely heavily forested. The lake ecosystem and water quality during this time showed little to no change, with algal productivity likely driven by a constant input of natural nutrients. Post Māori arrival, algal productivity was reduced suggesting an increase in water quality likely driven by added lake marginal plants providing a riparian buffer to terrestrially derived nutrients. Lake productivity increased dramatically post European arrival ~AD 1850, coeval with an increase in sediment Cd, suggesting that fertilisation may have driven a decline in water quality. Further increases in fertilisation and stocking rates indicate additional agricultural nutrient fluxes entering Lake Nganoke in AD 1950 when agriculture intensified. Abundances in denitrifying Gammaproteobacteria indicate increases in nutrient loading while bloom forming Cyanobacteria peak ~AD 2000 before declining till present. Riparian planting following Māori arrival appears sufficient to buffer the lake against increased terrestrial nutrient fluxes associated with land clearing. However, a riparian zone that covers the majority of the catchment post European settlement was inadequate in altering the lake’s degrading ecosystem and water quality trajectory.</p>

Biomarkers, stable carbon isotope, and trace element distribution of source rocks in the Orange Basin, South Africa: implications for paleoenvironmental reconstruction, provenance, and tectonic setting

Aptian to Campanian sediments from the Western offshore to Central Orange Basin were studied by integrating molecular geochemistry, inorganic and isotopic studies to recognize their geochemical characteristics via the reconstruction of the Orange basin’s paleoweathering, paleosalinity, paleovegetation, paleoclimate, and tectonic records. Molecular analyses of both aliphatic and aromatic compounds reveal an input dominantly from a marine source. The source rocks accumulated in a reduced, anoxic, saline water column. Based on various biomarker proxies and vitrinite reflectance data, some samples are thermally mature to produce petroleum, while others are not. According to the V/Ni ratio, samples from the Orange Basin in South Africa are mainly anoxic, with only a few samples ranging from suboxic to anoxic. This is congruent with biomarker and isotope analyses that further indicate the presence of marine-derived source rocks with some terrestrial remains generating hydrocarbons. The investigated sediments are made up of intermediate igneous rocks that have undergone moderate chemical weathering. Geochemical figures on tectonic setting discriminant function diagrams revealed a continental rift of passive margin settings. As a result, the extrapolated crustal processes are directly analogous to the genesis and evolution of the Orange Basin, demonstrating Gondwana’s breaking up and the opening of the Atlantic Ocean Margin.

Paleoenvironmental reconstruction of Triassic floras from the Central North Sea

The Triassic sediments of the Central North Sea (CNS) are considered to have been deposited in a continental environment under a semi-arid climate. The Skagerrak Formation in particular, comprises an alternation of sandstone and mudstone members, the development of which is considered to be climatically driven. However, conflicting models exist as to how climate influences member deposition. Here we analyse the climatic signal using a multivariate statistical approach in which de-trended correspondence analysis (DCA) is applied to palynological observations to quantify environmental reconstruction. Using DCA it has been possible to define paleoecological groups and construct a relative hydrological state trend showing hydrological conditions within the centre of the CNS basin during the Triassic. The resultant trends reveal that the relationship between hydrological conditions in the basin and the development of individual sandstones and mudstone members is perhaps not a simple as indicated by existing models. In particular our data suggest that whilst influenced by broader climate trends, in the basin centre, there is no simple relationship between climate change and sandstone/mudstone development. The data also indicates that the Julius and Jonathan mudstone members were deposited under differing hydrological conditions. The DCA trends shown here also suggest that the Carnian Pluvial Episode (CPE) documented from the South Permian Basin and Tethys is not expressed in the CNS.

Volcaniclastic lacustrine sedimentation in the Pleistocene Guayllabamba intermontane basin in the Ecuadorian Andes

In this work, we present the description of the sedimentary fill of a well-exposed lacustrine succession in the Ecuadorian Andes. The Guayllabamba basin is an intermontane basin located in the Andean range of Ecuador, and part of its sedimentary history is represented by a volcanically-influenced ∼100 m thick lacustrine unit of the Pleistocene age. We create a stratigraphic cross-section from the eastern to western lake margins and identify nineteen facies that were used to carry out a paleoenvironmental reconstruction. The Guayllabamba paleolake was developed in a tectonic depression surrounded by volcanoes and it was filled by sediments derived from the erosion of the volcanic edifices, the reworking of unconsolidated pyroclastic deposits, and deposition of pyroclastic currents into the lake. The lake shows a deepening trend, passing from shallow deltaic sedimentation to varved diatomites with turbidites. Abundant ash-fall beds, monolithological pumiceous deltaic sequences, and pumice-dominated thick ignimbrites show the impacts of volcanism on lacustrine sedimentation within this basin. Soft-sediment deformation and gravity flow deposits are common due to the intrabasinal tectonic activity and to the intrusion of a lava body. Aulacoseira-rich diatomites dominated the background lake sedimentation. The outcrops of the Guayllabamba basin are outstanding examples of the interaction between volcaniclastic and lacustrine sedimentation.