Using coralline algae to understand historic marine cloud cover

Global Change Biology, 2013

Marine pCO 2 enrichment via ocean acidification (OA), upwelling and release from carbon capture and storage (CCS) facilities is projected to have devastating impacts on marine biomineralisers and the services they provide. However, empirical studies using stable endpoint pCO 2 concentrations find species exhibit variable biological and geochemical responses rather than the expected negative patterns. In addition, the carbonate chemistry of many marine systems is now being observed to be more variable than previously thought. To underpin more robust projections of future OA impacts on marine biomineralisers and their role in ecosystem service provision, we investigate coralline algal responses to realistically variable scenarios of marine pCO 2 enrichment. Coralline algae are important in ecosystem function; providing habitats and nursery areas, hosting high biodiversity, stabilizing reef structures and contributing to the carbon cycle. Red coralline marine algae were exposed for 80 days to one of three pH treatments: (i) current pH (control); (ii) low pH (7.7) representing OA change; and (iii) an abrupt drop to low pH (7.7) representing the higher rates of pH change observed at natural vent systems, in areas of upwelling and during CCS releases. We demonstrate that red coralline algae respond differently to the rate and the magnitude of pH change induced by pCO 2 enrichment. At low pH, coralline algae survived by increasing their calcification rates. However, when the change to low pH occurred at a fast rate we detected, using Raman spectroscopy, weaknesses in the calcite skeleton, with evidence of dissolution and molecular positional disorder. This suggests that, while coralline algae will continue to calcify, they may be structurally weakened, putting at risk the ecosystem services they provide. Notwithstanding evolutionary adaptation, the ability of coralline algae to cope with OA may thus be determined primarily by the rate, rather than magnitude, at which pCO 2 enrichment occurs.

Geology, 2011

Bering Sea climate and ecosystem dynamics have recently undergone major changes that have affected seasonal sea ice distribution and marine life, including commercially important salmon fi sheries. Unfortunately, long-term Bering Sea dynamics are poorly understood, largely because of an absence of high-resolution marine proxy archives. Here we present the fi rst record compiled from annual growth-increment widths of long-lived coralline algae collected in shallow-water habitats spanning the entire Aleutian Islands. While algal growth in the Aleutians exhibits a variable relationship with regional temperatures, it is strongly driven by changes in solar radiation reaching the seafl oor. Therefore, it provides an exceptional archive of long-term light dynamics, which in the Bering Sea is attributed to changes in strength of the Aleutian Low (AL), the dominant climate pattern of the subarctic North Pacifi c. The AL is positively related to Bering Sea cloudiness and wind strength, which in turn fosters upper-ocean mixing. Mixing raises surfacewater nutrient concentrations and stimulates plankton production, which is positively linked to Alaskan salmon abundance. Enhanced clouds and plankton production increase shading on the shallow seafl oor and reduce algal growth. Light-driven algal growth rates track proxy-derived salmon abundance from 1782 onward, but are poorly related to temperature-dominated Pacifi c Decadal Oscillation (PDO) variability prior to the twentieth century. The algal record suggests that the present-day relationship of AL and PDO varied historically and that salmon stocks have been more closely related to AL strength via its effect on plankton abundance rather than PDO-related temperatures.

Biogeosciences, 2018

The shallow-marine benthic coralline alga Clathromorphum compactum is an important annual-to sub-annual-resolution archive of Arctic and subarctic environmental conditions, allowing reconstructions going back > 600 years. Both Mg content, in the high-Mg calcitic cell walls, and annual algal growth increments have been used as a proxy for past temperatures and sea ice conditions. The process of calcification in coralline algae has been debated widely, with no definitive conclusion about the role of light and photosynthesis in growth and calcification. Light received by algal specimens can vary with latitude, water depth, sea ice conditions, water turbidity, and shading. Furthermore, field calibration studies of Clathromorphum sp. have yielded geographically disparate correlations between MgCO 3 and sea surface temperature. The influence of other environmental controls, such as light, on Mg uptake and calcification has received little attention. We present results from an 11-month mesocosm experiment in which 123 wildcollected C. compactum specimens were grown in conditions simulating their natural habitat. Specimens grown for periods of 1 and 2 months in complete darkness show that the typical complex of anatomy and cell wall calcification develops in new tissue without the presence of light, demonstrating that calcification is metabolically driven and not a side effect of photosynthesis. Also, we show that both light and temperature significantly affect MgCO 3 in C. compactum cell walls. For specimens grown at low temperature (2 • C), the effects of light are smaller, with a 1.4 mol % MgCO 3 increase from low-light (mean = 17 lx) to highlight conditions (mean = 450 lx). At higher (10 • C) temperature there was a 1.8 mol % MgCO 3 increase from low to high light. It is therefore concluded that site-and possibly specimen-specific temperature calibrations must be applied, to account for effects of light when generating Clathromorphum-derived temperature calibrations.

Palaeogeography, Palaeoclimatology, Palaeoecology

The Bay of Brest (BB) is a mixed, tide-dominated estuarine system. The shore terraces of this bay are occupied by modern free-living (calcareous) coralline algae locally termed "maerl", organized in bed-like morphologies (rhodolith deposits). Cores retrieved from around the bay reveal fossilized primitive maerl beds of Holocene age, interbedded in sandy-silt sedimentation. The alternation between biogenic constructions and estuarine sedimentation may provide evidence of varying environmental conditions of the late-Holocene period. This paper mainly focuses on the results of chronostratigraphic and biosedimentological interpretations of coring data collected in less than 15 m of water depth in an attempt to decipher the main stages of maerl colonization in the bay. In particular, this study raises several significant points allowing to draw links between centennial to millennial-scale climatic changes in marine estuary sedimentation and episodes within the development of maerl biocenoses. The paleo-bathymetry of the coastal terraces has not changed significantly over the last 5000 years. Yet, the first maerl occurrence only appeared around 2000 cal yr B.P., likely showing that the environmental conditions were not favorable for their emergence prior to that time. Pioneer maerl beds developed on coarse shell deposits inherited from the paleostorms affecting the Atlantic coasts during the colder climatic period of the Iron Age (3100-1950 cal yr B.P.). The accumulations then aggraded at various and discontinuous rates, Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. sometimes reaching up to 2.1 m/kyr. Maerl beds temporarily disappeared in the southern part of the Bay of Brest when sedimentation rates increased throughout the bay during the Dark-Age cold period (1375-1250 cal yr B.P.), suggesting that maerl formations could not keep up with sedimentation rate exceeded a certain threshold. Muddy sedimentation conditions also dramatically changed on two occasions, with the establishment of coarse storm levels, set at the intervals 825-600 cal yr B.P. (MWP) and 113-0 cal yr B.P. But maerl deposits reseed the environment as a result of each new cold period, demonstrating the persistence of such coralline algae against drastic palaeoenvironmental changes in coastal areas. Highlights ► Stratigraphy of late-Holocene estuarine sediments reveals interbedded maerl beds. ► First maerl occurrence in the Bay of Brest is dated around 2000 cal yr BP. ► Development of maerl beds coincides with the onset of colder and drier climates. ► Maerl building phases are disrupted by periods of climate deterioration. ► Coarse sedimentary deposits are associated with increased paleostorm activity.

Paleoceanography and paleoclimatology, 2021

This alarming rate of decline has potentially devastating impacts on Arctic ecosystems, and destabilizing effects on ocean circulation, global climate, and human populations due to the connection of sea ice to multiple feedback mechanisms including the ice-albedo feedback (Meier et al., 2014). However, current climate model projections are unable to fully capture annual sea ice variability and often underestimate the amount of sea ice decline due to a limited understanding of the internal and anthropogenic