The Crawford Lake biosphere evolved in response to both natural and anthropogenic stressors since water filled this karstic basin on the Niagara Escarpment. It was substantially impacted by hydrologic/limnological changes attributed to environmental conditions that define the Northgrippian and Meghalayan Ages, but the greatest impact was human activity in its small catchment. Cultural eutrophication from Indigenous agriculture in the late 13th century altered the lake chemistry, promoting seasonal precipitation of calcite that allows sub-annual resolution. Global signatures of the Great Acceleration are recorded in varved sediments deposited since the mid-20th century, despite little direct human impact on the Crawford Lake catchment since 1900 CE. A sharp increase in green algae and chrysophytes that rely on passive diffusion of CO2 for photosynthesis closely tracks global CO2 emissions concentrations since the mid-20th century. Elevated pCO2 affects lake biospheres in numerous and complex ways, with synergistic responses with limiting nutrients. The reported widespread increase in both groups of non-RuBisCO algae suggests that algal phyla limited by Holocene CO2 concentrations are favoured by atmospheric conditions not experienced since the middle Miocene. Novel lake biospheres are an additional argument for adding an Anthropocene epoch and Crawfordian age to the geologic time scale. This article is part of the theme issue 'The biosphere in the Anthropocene'.

Four years after the Anthropocene Working Group (AWG) voted to work toward defining the Anthropocene series/epoch with a base in the mid-20th C, the varved sediments of Crawford Lake (Milton, ON, Canada) were selected as the Global boundary Stratotype Section and Point (GSSP) candidate. The initial major rise in activity of 239 + 240 Pu had been selected as the primary chronostratigraphic marker to define the base of the Anthropocene, but the precise year when this occurred could not be determined from measurements of samples combining multiple varves. Individual varves from freeze cores collected in April 2023 provide annual resolution for bomb radionuclides, allowing the varve age model to be refined, former assignments determined to have been 1 year too old. The increase in 239 + 240 Pu activities (calculated from atom concentrations of 239 Pu and 240 Pu measured using Accelerated Mass Spectrometry) of 0.0031 Bq/g between varves now assigned to 1951 and 1952 is consistent with the onset of thermonuclear weapons testing on November 1, 1952, so the proposed base for the Anthropocene is at the contact between the light- and dark-coloured laminae deposited in 1952 CE (17.5 cm in core CRA23-BC-1F-B). Sharply lower 239 + 240 Pu and 137 Cs activities capture the moratorium from November 1958 to September 1961 before rising quickly to peak activities of 239 + 240 Pu in 1963 CE. Analysis of individual varves with varying amounts of organic matter and inorganic calcite illustrates the influence of lithology on organic proxies, but the upcore trend toward depleted values of δ 15 N through the 20th C reflects increased fossil fuel combustion worldwide. An inflection point in δ 15 N around 1911 CE is attributed the global impact of the Haber-Bosch process and establishment of nearby steel mills, and another in the early 1950s attributed to the Great Acceleration to which the tipping point in the Earth system is attributed.

Spheroidal carbonaceous particles (SCPs) are formed from the incomplete, high-temperature combustion of fossil fuels. They are transported to a variety of depositional environments downwind of their sources and thus have the potential to be used to measure human activity on a regional scale. Composed mainly of elemental carbon, these fly ash particles are chemically inert and survive acid treatment, including HF. However, unlike microcharcoal, SCPs are typically overlooked during palynological analysis. Both types of black carbon are common in palynological preparations of varved sediments from Crawford Lake, Ontario, Canada where they can be correlated with the historic record of land use over the past two centuries. Increases in microcharcoal concentration correlate with historic records of land clearing in the early-mid nineteenth century and logging and lumber milling between 1885 and 1957 CE. The rapid increase in SCP concentration during the mid-twentieth century is attributed to the global increase in fossil fuel combustion and industrial activity (the Great Acceleration) and the decline during the early 1980s records increasingly stringent air quality standards as well as decreased demand for steel (and coking coal) in nearby Hamilton. Palynologists are urged to pay attention to these useful proxies of fossil fuel combustion in their slides.

Multiproxy analysis of sedimentary records retrieved from the three basins of Walden Pond, Concord, Massachusetts, reveals distinct sedimentary processes characterizing each basin configuration. It also allows reconstruction of a comprehensive landscape history that explores a wide range of questions from climate change to regional anthropogenic and natural events. Here, we present an 800-year-long sedimentary record of the three basins of Walden Pond, a closed kettle lake, that has been affected by changes to the landscape since European settlement in the early 17th century and during later transition to a popular tourist destination. Separate age models were developed for each basin using pollen stratigraphy, onset of industrial contaminants, and radiocarbon dating, which allow robust correlation between the three basins. Using a combination of geophysical, sedimentological, geochemical, and palynological proxies we were able to define four time periods of landscape change: a mostly forested landscape before the early 17th century, an early European era characterized by logging and shoreline use, an industrial period with peak concentrations of air pollutants such as coal and Pb, and the youngest period of widespread recreational activities marked by soil erosion, high nutrient input, and high productivity. While all three basins show the main trends, the shallowest basin is most affected by shoreline processes. The deepest and largest basin has the highest sedimentation rate, likely because of sediment focusing and more effective preservation of organic matter due to partial lake-bottom anoxia. Suspended sediments and airborne pollutants are more equally distributed throughout all basins but can be diluted in larger basins. In addition to long-term trends, we were able to identify sudden-onset sedimentation events, likely caused by mass wasting along the steep-sided slopes of all three basins. Three of these horizons are evident in more than one basin and perhaps are linked to a strong historic earthquake in 1755 CE and two prehistoric earthquakes.

Holleford Crater is a deeply buried, 2.35 km diameter late Proterozoic-early Cambrian (550 +/- 50 Ma) simple impact crater located in southeastern Ontario, Canada. Exploration drilling in the 1950-60s indicated a >450 m deep, simple impact structure with an infill stratigraphy of Cambro-Ordovician clastic and carbonate sediments and a -2.2 mGal gravity anomaly. We conducted new ground-based geophysical surveys (magnetics, gravity) and potential field modeling to better resolve the buried impact structure depth, subsurface geometry, and postimpact modification. Geophysical surveys reveal a well-defined similar to 3 mGal Bouguer gravity low and <20 nT residual magnetic anomaly over the crater basin. The lack of a well-defined magnetic anomaly is due to the low magnetic contrast between Mesoproterozoic metasedimentary target rocks and Paleozoic infill sediments. The modeled basement surface shows a deeply buried (>400 m), eroded simple impact structure with a rim-to-rim diameter (D) of 1.8-2 km, a residual rim height of about 30 m and a true depth (d(t)) >400 m. The modeled diameter is smaller than the previous estimate (2.35 km) based on the surface outcrop pattern of Paleozoic strata, which overestimates the buried impact structure dimensions. The modeled basement surface identifies a rim breach and a possible fluvial outflow channel in the southeast impact structure rim. The channel is up to 150 m deep and 400 m in width and has morphology similar to outlet channels produced by fluvial rim dissection of terrestrial impact structures and "tadpole craters" on Mars.

Abstract The Charity Shoal structure is a circular, ∼1.2‐km‐diameter, bedrock‐rimmed shoal in eastern Lake Ontario with a ∼20‐m‐deep central basin. The structure has been proposed as a possible Middle Ordovician impact crater or volcanic intrusion. We conducted marine seismic and magnetic surveys (9‐km2) and 3‐D geophysical modeling to better resolve the Charity Shoal subsurface geology and possible origins. Three models were evaluated: (a) a buried (>450 m) impact structure in Mesoproterozoic basement, (b) a maar‐diatreme, (c) a cylindrical, zoned volcanic plug. Seismic profiles and multi‐beam bathymetry revealed >30 m of Quaternary sediments overlying Middle Ordovician (Trenton Group) carbonate bedrock and complex, 3‐dimensional folding and faulting of the structure rim. Magnetic surveys recorded an annular magnetic high (>600 nT) over the structure rim and a central magnetic low (∼500–600 nT) coincident with a ∼−1.7 mGal Bouguer gravity anomaly. The continuity of Trenton Group strata in seismic profiles rules out a previously proposed Mesozoic maar‐diatreme intruded into Paleozoic strata. The zoned volcanic plug model reproduced the annular magnetic anomaly but was incompatible with Bouguer gravity profiles. The magnetic anomaly was best reproduced by a simple impact structure seated in Mesoproterozoic basement at 450–500 m depth with a rim‐to‐rim diameter of ∼1.2 km and rim height of ∼10–20 m. A 100‐m wide and 50‐m‐deep channel in the Mesoproterozoic basement may record fluvial dissection of the southwestern rim. A buried (>450 m), simple impact crater is most compatible with all available geophysical data at Charity Shoal.

Varved sediments in meromictic Crawford Lake consist of dark–light couplets of organic matter (primarily phytoplankton and amorphous organic matter) capped by calcite crystals. The crystals precipitate in the alkaline epilimnion between spring and fall turnover, consistent with Langelier Saturation Index calculations that predict calcite precipitation when pH and temperature exceed 7.76 and ~ 15 °C, respectively. Climate, primary production, and the pH of the epilimnion control lamina thickness: acid rain primarily affects the precipitation and accumulation of calcite crystals, whereas both endogenic calcite and authigenic organic matter are affected by climate and primary production. Thin varves, often with barely perceptible light-coloured calcite laminae were deposited between the late 1940s and mid-1970s, when the pH of the epilimnion fell slightly in response to deterioration in air and water quality associated with rapid industrialization. Conditions required for precipitation of calcite laminae were absent during the sixteenth to mid-nineteenth centuries, an interval corresponding to the Little Ice Age when no human impact affected the catchment. Varves dating from 1867 CE onwards (the Canadian Zone) facilitate the candidacy of the deep basin sediments of Crawford Lake to define the Anthropocene epoch.

An annually laminated succession in Crawford Lake, Ontario, Canada is proposed for the Global boundary Stratotype Section and Point (GSSP) to define the Anthropocene as a series/epoch with a base dated at 1950 CE. Varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters reflect environmental change at global to local scales. Spheroidal carbonaceous particles and nitrogen isotopes record an increase in fossil fuel combustion in the early 1950s, coinciding with early fallout from nuclear and thermonuclear testing – 239+240Pu and 14C:12C, the latter more than compensating for the effects of old carbon in this dolomitic basin. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration, and calcite precipitation was reduced, producing thin calcite laminae around the GSSP that is marked by a sharp decline in elm pollen (Dutch Elm disease). The lack of bioturbation in well-oxygenated bottom waters, supported by the absence of fossil pigments from obligately anaerobic purple sulfur bacteria, is attributed to elevated salinities and high alkalinity below the chemocline. This aerobic depositional environment, highly unusual in a meromictic lake, inhibits the mobilization of Pu, the proposed primary stratigraphic guide for the Anthropocene.

Liman Tepe-Clazomenae, located in the southern Bay of Izmir, Turkey, was an important Early Bronze Age to Classical Period trading port and cultural centre in the eastern Aegean. The mainland harbour, now submerged similar to 1.5-2 m below present sea level, is one of the best-preserved examples of an Iron Age (Archaic Period; ca. 7th-6th c. BCE) semi-enclosed harbour (>5 ha) with engineered breakwater structures. A multi-proxy study (micropalaeontology, micro-XRF core scanning) was conducted on seven harbour sediment cores and integrated with geophysical data to map the harbour structures and document coastal palaeoenvironmental changes. Bathymetry and side-scan mapping revealed two broad (>35 m) rubble-constructed breakwater structures and a submerged headland that divided the harbour into two separate sub-basins. Linear magnetic anomalies within the eastern breakwater indicate a buried pier structure, recording possible augmentation of a Late Bronze Age (LBA) or Early Iron Age (EIA) proto-harbour embayment. The harbour basin stratigraphy comprises foreshore and upper shoreface deposits overlying terrigenous clays across a marine transgressive surface. A distinctive siltrich chemofacies with increased Ti/Ca and decreased Si marks a transition from a sandy marine shoreface to a low energy, sheltered LBA proto-harbour embayment. The Iron Age harbour construction (ca. 7th-6th c. BCE) is recorded by a rise in Rosalina, decreased Ti/Ca and the appearance of Archaic pottery. The harbour was in use from the Archaic to early Classical periods and served as Clazomenae's mainland commercial port.

Abstract Varved sediments in meromictic Crawford Lake consist of dark-light couplets of organic matter (primarily phytoplankton and amorphous organic matter) capped by calcite crystals. The crystals precipitate in the alkaline epilimnion between spring and fall turnover, consistent with Langelier Saturation Index calculations that predict calcite precipitation when pH and temperature exceed 7.76 and ~ 15°C respectively. Climate, primary production, and acid precipitation control lamina thickness: acid precipitation primarily affects the precipitation and accumulation of calcite crystals, whereas both endogenic calcite and authigenic organic matter are affected by climate and primary production. Thin varves, often with barely perceptible light-coloured calcite lamina were deposited between the late 1940s and mid-1970s, when air and water quality were impacted by rapid industrialization. Conditions required for precipitation of calcite laminae were absent during the 16th to mid-19th centuries, an interval corresponding to the Little Ice Age when no human impact occurred in the catchment. Varves dating from 1867 CE onwards (the Canadian Zone) facilitate the candidacy of the deep basin sediments of Crawford Lake to define the Anthropocene epoch.

Rising post-glacial sea levels had a major influence on the prehistoric settlement of the Aegean coastal zone. At Liman Tepe, an important Chalcolithic-Bronze Age coastal settlement on the south coast of the Bay of Izmir, archaeological evidence suggests a Neolithic (ca. 9600-5500 BCE) presence, but no settlement has been discovered on land. Sea levels during the Neolithic period were between 6 and >20 m below present and there is high potential for discovery of submerged prehistoric sites. Marine sediment coring and geophysical investigations (bathymetry, sub-bottom seismic profiling; >600 line-km) were conducted over a 4-km(2) inshore area to assess the underwater archaeological potential. Multi-proxy sediment analysis (sedimentary facies, micropalaeontology, micro-XRF geochemistry) was conducted on 20 cores to reconstruct the relative sea level (RSL) history and coastal palaeogeography. Palaeoshoreline positions were estimated by back-stripping of the decompacted sediment thickness from a digital bathymetric model (DBM). The DBM reveals a drowned middle Holocene coastal plain with well-preserved relict river channels, palaeoshorelines and coastal headlands. The inshore stratigraphy consists of shoreface, foreshore and lagoonal deposits overlying terrestrial clay and palaeosols, defining a marine transgressive surface (MTS). The MTS records the inundation of the coastal plain prior to ca. 4000 BCE (transgressive systems tract; TST) and is marked in cores by an increasing abundance of foraminifera and a rise in Ca/Ti. During the Early Neolithic (ca. 6700 BCE), the shoreline was >500 m seaward (RSL similar to -14 to -16 m) and Karantina Island was a broad coastal headland with a sheltered western embayment. By the Middle Chalcolithic (ca. 4800 BCE), the coastline had transgressed similar to 800 m inland of the present shoreline and the Liman Tepe headland was separated from the mainland by a shallow coastal wetland. The maximum transgression (similar to 1 km inland at ca. 4000 BCE) was followed by a shift to a high-stand systems tract (HST) and rapid coastline progradation by barrier accretion and lagoon development. Palaeogeographic maps identify areas with high underwater archaeological potential: 1) palaeoriver channels and lowland riverine habitats formed during the TST, prior to 4000 BCE, 2) submerged palaeoshorelines and coastal promontories (water depths 10-14 mbsl) with high potential for Neolithic sites, and 3) protected coastal embayments and lagoons representing possible prehistoric anchorage sites. (C) 2021 Elsevier Ltd. All rights reserved.

Lechaion's inner harbour basin was constructed in the 7th-6th c. BCE and served as Corinth's principal port for over a millennium. The harbour decline and abandonment in the 6th c. CE has been attributed to several causes: natural siltation, co-seismic uplift, coastal subsidence, and damage by tsunami impacts. A multi-proxy palaeoenvironmental study was conducted on seven cores from Lechaion's inner harbour to determine changes in the coastal environments and timing and cause of harbour abandonment. Palaeoenvironments were reconstructed using high-resolution micro-XRF core scanning of sedimentary facies, isotopic (delta O-18, delta C-13), and micropalaeontological analyses (foraminifera, palynomorphs). The harbour lithostratigraphy consists of an uppermost (similar to 1 m) sequence of laminated mud and marl overlying interbedded pebbly sand and mud containing abundant marine microfossils and Roman pottery refuse. A thin (<12 cm) calcrete layer at the base of the marl defines a basin-wide paraconformity, marking a transition from a marine-estuarine harbour basin to a restricted, evaporitic lake. Basin restriction is recorded by a sharp decline in terrigenous elements (Si, Ti, K, Fe), increased Sr, delta O-18, a decline in foraminifera and marine dinoflagellate cysts, and an increase in freshwater algae. The event is constrained by AMS C-14 age modelling to the 6th c. CE and interpreted as rapid, co-seismic uplift of the harbour floor, most likely during destructive earthquakes of 524 and 551/552 CE. These seismic events have been linked to a similar to 1.1 m uplift of the nearby Perachora Peninsula and sediment liquefaction structures on-site. No evidence was found for 2nd c. BCE or 6th c. CE tsunami events proposed in previous work. This study represents the most comprehensive geoarchaeological study completed to date in Lechaion's inner harbour and confirms its destruction and abandonment in the 6th c. CE as a result of co seismic uplift and rapid shoaling of the inner basin. (C) 2021 Elsevier Ltd. All rights reserved.

The SciencesVolume 41, Issue 1 p. 9-13 A Tale of Two Lakes ERICA B. GOLDMAN, ERICA B. GOLDMAN Erica B. Goldman: is a doctoral candidate in zoology at the University of Washington in Seattle.Search for more papers by this author ERICA B. GOLDMAN, ERICA B. GOLDMAN Erica B. Goldman: is a doctoral candidate in zoology at the University of Washington in Seattle.Search for more papers by this author First published: 31 July 2013 https://doi.org/10.1002/j.2326-1951.2001.tb03542.x AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume41, Issue1January‐February 2001Pages 9-13 RelatedInformation