Posts Tagged 'paleo'

Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia

Highlights

• Ocean warming has accelerated since the 1970s in the nearshore Kimberley.

• Coral calcification remains less affected and ‘normal’ seasonal coral internal carbonate chemistry is observed.

• Under intensified warming, coral’s ability to concentrate metabolic DIC has been reduced.

• Ocean acidification has led to the secular reduction of pHcf.

Abstract

The impact of climate changes on corals living in naturally extreme environments is poorly understood but crucial to longer-term sustainability of coral reefs. Here we report century-long temperature (Sr/Ca and Li/Mg) and calcifying fluid (CF) carbonate chemistry (δ11B and B/Ca) records for a long-lived (1919 to 2016) Porites coral from the high thermally variable Kimberley region of northwestern Australia. We investigate how increasing temperatures and ocean acidification are manifested in the carbonate chemistry of coral’s CF and impacts of climate change on calcification. Using Sr/Ca and Li/Mg multiproxy we show that annual temperature in the nearshore Kimberley exhibited a gradual increase (0.009 ± 0.003 °C/yr) from the 1920s onward. However for the most recent years (2000–2015) more rapid summer warming (0.05 ± 0.01 °C/yr) are registered, indicative of intensified warming. Despite that, we find no significant trend for calcification rate of this coral over the past century, as well as ‘normal’ seasonal variability in coral’s CF carbonate chemistry. Importantly, the coral’s ability to concentrate inorganic carbon seems to be affected by recent warming, with reduced DICcf observed during 2008 to 2015, while the minimally-affected pHcf acts to compensate the decreases of DICcf with the calcification rate showing only slight decrease. Additionally, we also find that ocean acidification has clearly led to the long-term reduction in the pH of the CF.

Continue reading ‘Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia’

Geochemistry of upper Permian siliceous rocks from the Lower Yangtze region, southeastern China: implications for the origin of chert and Permian ocean chemistry

The Permian Chert Event is of great significance to understanding the geological evolution of the entire Permian; however, the origin of widespread chert formation is debated. We report new geochemical data from deep-marine siliceous rocks of the upper Permian Da-long Formation, Lower Yangtze region, southeastern China. Their geochemical results show that these thin-bedded siliceous rocks have a clear biologic origin, with rare to no evidence of hydrothermal influence. The values of Al/(Al + Fe + Mn) and Eu/Eu* are 0.60–0.84 (mean = 0.72) and 0.45–1.08 (mean = 0.77), respectively, and Mn/Ti ratios are relatively low (mean = 0.72). The correlations of LaN/CeN, LaN/YbN, and Fe2O3/TiO2 with Al2O3/(Al2O3 + Fe2O3), along with the Ce anomaly, indicate that the Da-long siliceous rocks were deposited at a transitional zone between a continental margin and the open ocean; i.e., relatively close to terrestrial sediment input and far from hydrothermal activity. The accumulation of chert is related to its unique paleogeographic location in an equatorial setting with many submarine paleo-highlands. Intense upwelling and frequent local volcanism are the main factors that promoted the development of siliceous rocks in the studied area. Ocean acidification triggered by large-scale volcanism (Large Igneous Province) during the late Permian led to extensive silica precipitation and preservation.

Continue reading ‘Geochemistry of upper Permian siliceous rocks from the Lower Yangtze region, southeastern China: implications for the origin of chert and Permian ocean chemistry’

Calibration of the pH-δ11B and temperature-Mg/Li proxies in the long-lived high-latitude crustose coralline red alga Clathromorphum compactum via controlled laboratory experiments

A solid understanding of global oceanic change throughout Holocene time is needed to contextualize and interpret recent observations of rapid warming (Moore, 2016), ocean acidification (Popova et al., 2014Qi et al., 2017), increasing meltwater input (Halfar et al., 2013Notz and Stroeve, 2016) and circulation changes (Liu et al., 2017Rahmstorf et al., 2015Yang et al., 2016) in the Arctic and subarctic Oceans. Precisely reconstructing acidification and temperature variations throughout the Holocene will provide a vital context for interpreting current environmental changes and future climate projections in the region. However, existing paleoenvironmental reconstructions are sparse and uncertain, largely owing to limited availability of high fidelity paleoceanographic archives, such as marine carbonates, in high latitude waters. Coralline algae of the genus Clathromorphum have emerged as key candidates for reconstructing high-latitude environmental variability at annual to sub-annual resolution. Here, we present the first empirical calibrations of boron isotope-pH and Mg/Li-temperature relationships within the long-lived, crustose coralline red alga Clathromorphum compactum. Calibration experiments were performed in triplicate, growing wild-collected specimens for four months at three controlled temperatures (6.4 – 12.4 oC) and four pCO2 conditions (352 – 3230 ppm), to test the effects of these environmental parameters on the isotopic and elemental composition of the algal skeleton.We find that boron isotopes within the skeleton of C. compactum (δ11Bcc) are well correlated with δ11B of seawater borate (δ11Βborate), defining the following equation: δ11Βcc (2σ) = 1.46 (0.06) δ11Βborate + 6.91 (0.72). This equation can be used to reconstruct δ11Βborate of the coralline alga’s ambient seawater, from which past seawater pH can be calculated. We also identified a strong correlation between skeletal Mg/Li ratio and seawater temperature, defined by the equation: Mg/Li (2σ) = 0.17 (0.02) temperature (oC) + 1.02 (0.16). Therefore, despite the strong biological control that this species appears to exert on calcification site pH (elevated 1.0-1.6 pH units above seawater pH, inferred from δ11Bcc > δ11Βborate), and the apparent relationship between skeletal extension rate and skeletal Li/Ca and Mg/Ca, the δ11Bcc and Mg/Li ratios of the coralline alga’s skeleton strongly and significantly respond to ambient seawater pH and temperature, respectively. These results support the use of δ11B and Mg/Li within C. compactum for pH and temperature reconstructions of northern high-latitude oceans.

Continue reading ‘Calibration of the pH-δ11B and temperature-Mg/Li proxies in the long-lived high-latitude crustose coralline red alga Clathromorphum compactum via controlled laboratory experiments’

Carbonate dissolution enhanced by ocean stagnation and respiration at the onset of the Paleocene‐Eocene Thermal Maximum

The Paleocene‐Eocene Thermal Maximum was a transient, carbon‐induced global warming event, considered the closest analog to ongoing climate change. Impacts of a decrease in deepwater formation during the onset of the Paleocene‐Eocene Thermal Maximum suggested by proxy data on the carbon cycle are not yet fully understood. Using an Earth System Model, we find that changes in overturning circulation are key to reproduce the deoxygenation and carbonate dissolution record. Weakening of the Southern Ocean deepwater formation and enhancement of ocean stratification driven by warming cause an asymmetry in carbonate dissolution between the Atlantic and Pacific basins suggested by proxy data. Reduced ventilation results in accumulation of remineralization products (CO2 and nutrients) in intermediate waters, thereby lowering O2 and increasing CO2. As a result, carbonate dissolution is triggered throughout the water column, while the ocean surface remains supersaturated. Our findings contribute to understanding of the long‐term response of the carbon cycle to climate change.

Continue reading ‘Carbonate dissolution enhanced by ocean stagnation and respiration at the onset of the Paleocene‐Eocene Thermal Maximum’

Global bioevents and the Cretaceous/Paleogene boundary in Texas and Alabama: stratigraphy, correlation and ocean acidification

Highlights
• This paper discusses the K/Pg in terms of surface water acidification caused by the K/Pg impact event. This is coupled with a new model for, and correlation of, the events recorded in a number of areas both proximal to the impact and distal. In particular the model is based on fieldwork in Texas.

Abstract
With increasing levels of atmospheric pCO2 the oceans are becoming progressively more acidic, with the impact of a lowered pH beginning to affect the calcification of numerous invertebrate groups, including foraminifers, pteropods, heteropods and calcareous nannoplankton. Research on the ecology of foraminifera in the Mediterranean Sea, Gulf of California, Caribbean Sea and elsewhere has shown how modern assemblages are responding to acidification. Experimental work in mesocosms and laboratory cultures are also adding to our knowledge of the response to pH changes. Near Ischia (Italy), natural CO2 vents amongst sea grass meadows are creating low pH environments in which it is possible to observe the response of benthic foraminifera. At a pH of 7.8 the foraminiferal assemblages are already becoming less diverse and below pH 7.6 there are often no calcite-secreting benthic foraminifera. In the Gulf of California, in a deeper-water setting, natural CO2 (and methane) vents are also lowering sea floor pH. The foraminifera show the impact of this change, although the relatively high carbonate saturation ensures that calcite-secreting foraminifers are able to live and reproduce in these relatively low pH environments, only becoming impacted by dissolution effects once dead. Using data from the Cretaceous–Paleogene boundary in Texas, Alabama and north-west Europe it is clear that the plankton was severely impacted by surface water acidification while the relatively shallow water benthic foraminifera show little change and no visible signs of post-mortem dissolution due to ocean acidification.

Continue reading ‘Global bioevents and the Cretaceous/Paleogene boundary in Texas and Alabama: stratigraphy, correlation and ocean acidification’

Dynamic storage of glacial CO2 in the Atlantic Ocean revealed by boron [CO3] and pH records

Highlights

• δ11 B and B/Ca data from benthic foraminifera can observe deep ocean carbon storage.

• Glacials exhibit a carbonate chemocline between shallow and deep water.

• East and West Atlantic basin exhibit differential carbonate system behaviour.

• 3 distinct states of [CO] stratification exist in the Atlantic glacial cycle.

• The level of Atlantic stratification is linked to atmospheric CO2 levels.

Abstract

The origin and carbon content of the deep water mass that fills the North Atlantic Basin, either Antarctic Bottom Water (AABW) or North Atlantic Deep Water (NADW) is suggested to influence the partitioning of CO2 between the ocean and atmosphere on glacial–interglacial timescales. Fluctuations in the strength of Atlantic meridional overturning circulation (AMOC) have also been shown to play a key role in global and regional climate change on timescales from annual to millennial. The North Atlantic is an important and well-studied ocean basin but many proxy records tracing ocean circulation in this region over the last glacial cycle are challenging to interpret. Here we present new B/Ca-[CO3] and boron isotope-pH data from sites spanning the North Atlantic Ocean from 2200 to 3900 m and covering the last 130 kyr from both sides of the Mid-Atlantic Ridge. These data allow us to explore the potential of the boron-based proxies as tracers of ocean water masses to ultimately identify the changing nature of Atlantic circulation over the last 130 kyr. This possibility arises because the B/Ca and boron isotope proxies are directly and quantitatively linked to the ocean carbonate system acting as semi-conservative tracers in the modern ocean. Yet the utility of this approach has yet to be demonstrated on glacial–interglacial timescales when various processes may alter the state of the deep ocean carbonate system. We demonstrate that the deep (∼3400 m) North Atlantic Ocean exhibits considerable variability in terms of its carbonate chemistry through the entirety of the last glacial cycle. Our new data confirm that the last interglacial marine isotope stage (MIS) 5e has a similar deep-water geometry to the Holocene, in terms of the carbonate system. In combination with benthic foraminiferal δ13C and a consideration of the [CO3] of contemporaneous southern sourced water, we infer that AABW influences the eastern abyssal North Atlantic throughout the whole of the last glacial (MIS2 through 4) whereas, only in the coldest stages (MIS2 and MIS4) of the last glacial cycle was AABW an important contributor to our deep sites in both North Atlantic basins. Taken together, our carbonate system depth profiles reveal a pattern of changing stratification within the North Atlantic that bears strong similarities to the atmospheric CO2 record, evidencing the important role played by ocean water mass geometry and the deep ocean carbonate system in driving changes in atmospheric CO2 on these timescales.

Continue reading ‘Dynamic storage of glacial CO2 in the Atlantic Ocean revealed by boron [CO3] and pH records’

Atmospheric carbon dioxide reconstruction and ocean acidification deduced from carbon isotope variations across the Triassic–Jurassic boundary in the Qiangtang Area, Tibetan Plateau

The end-Triassic mass extinction was one of the five most profound Phanerozoic extinction events. This event was accompanied by a series of significant environmental changes, of which the most notable is the emergence of warm climate and the world-wide disappearance of carbonate platform. C isotope is one of the main means of reconstructing palaeoenvironment, however, there are very
limited studies on Asia and Oceania in the East Tethys region. In China, continuous marine strata through the J/T boundary are widespread in the Qiangtang area of Tibet (Chen Lan et al., 2017), which provide us abundant
research materials to study the environmental geological evolution during the T–J transition in Asian and even eastern Tethys.

Continue reading ‘Atmospheric carbon dioxide reconstruction and ocean acidification deduced from carbon isotope variations across the Triassic–Jurassic boundary in the Qiangtang Area, Tibetan Plateau’


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