Phytoplankton calcification in a high-CO2 world

Ocean acidification in response to rising atmospheric CO2 partial pressures is widely expected to reduce calcification by marine organisms. From the mid-Mesozoic, coccolithophores have been major calcium carbonate producers in the world's oceans, today accounting for about a third of the total marine CaCO3 production. Here, we present laboratory evidence that calcification and net primary production in the coccolithophore species Emiliania huxleyi are significantly increased by high CO2 partial pressures. Field evidence from the deep ocean is consistent with these laboratory conclusions, indicating that over the past 220 years there has been a 40% increase in average coccolith mass. Our findings show that coccolithophores are already responding and will probably continue to respond to rising atmospheric CO2 partial pressures, which has important implications for biogeochemical modeling of future oceans and climate.     

Evidence for upwelling of corrosive "acidified" water onto the continental shelf

The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of approximately 40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area.     

Coral reefs under rapid climate change and ocean acidification

Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2 degrees C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef-associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled-up management intervention and decisive action on global emissions are required if the loss of coral-dominated ecosystems is to be avoided.     

CO 2驱动的海洋酸化对海洋生物多样性的影响研究进展

海洋酸化状况是全球海洋生物多样性的威胁之一。在海洋快速酸化的影响下,海洋生物物种丰度发生变化,从而改变海洋生物群落结构;缓慢的海洋酸化,使海洋生物具有一定的适应能力,但是与海洋生物生境息息相关,海洋酸化的间接影响成为生态的关键。对近年来海洋酸化对海洋生物多样性的影响进行了综述,并对海洋生物应对海洋酸化存在的问题进行了分析。     

Impact of anthropogenic CO2 on the CaCO3 system in the oceans

Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans. This acidification process has changed the saturation state of the oceans with respect to calcium carbonate (CaCO3) particles. Here we estimate the in situ CaCO3 dissolution rates for the global oceans from total alkalinity and chlorofluorocarbon data, and we also discuss the future impacts of anthropogenic CO2 on CaCO3 shell-forming species. CaCO3 dissolution rates, ranging from 0.003 to 1.2 micromoles per kilogram per year, are observed beginning near the aragonite saturation horizon. The total water column CaCO3 dissolution rate for the global oceans is approximately 0.5 +/- 0.2 petagrams of CaCO3-C per year, which is approximately 45 to 65% of the export production of CaCO3.     

Anthropogenic CO2 uptake by the ocean based on the global chlorofluorocarbon data set

We estimated the oceanic inventory of anthropogenic carbon dioxide (CO2) from 1980 to 1999 using a technique based on the global chlorofluorocarbon data set. Our analysis suggests that the ocean stored 14.8 petagrams of anthropogenic carbon from mid-1980 to mid-1989 and 17.9 petagrams of carbon from mid-1990 to mid-1999, indicating an oceanwide net uptake of 1.6 and 2.0 +/- 0.4 petagrams of carbon per year, respectively. Our results provide an upper limit on the solubility-driven anthropogenic CO2 flux into the ocean, and they suggest that most ocean general circulation models are overestimating oceanic anthropogenic CO2 uptake over the past two decades.     

Enhanced modern heat transfer to the Arctic by warm Atlantic Water

The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early-21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming.     

Foraminiferal calcification response to glacial-interglacial changes in atmospheric CO2

A record of foraminiferal shell weight across glacial-interglacial Termination I shows a response related to seawater carbonate ion concentration and allows reconstruction of a record of carbon dioxide in surface seawater that matches the atmospheric record. The results support suggestions that higher atmospheric carbon dioxide directly affects marine calcification, an effect that may be of global importance to past and future changes in atmospheric CO2. The process provides negative feedback to the influence of marine calcification on atmospheric carbon dioxide and is of practical importance to the application of paleoceanographic proxies.     

Biogeochemical Controls and Feedbacks on Ocean Primary Production

Changes in oceanic primary production, linked to changes in the network of global biogeochemical cycles, have profoundly influenced the geochemistry of Earth for over 3 billion years. In the contemporary ocean, photosynthetic carbon fixation by marine phytoplankton leads to formation of approximately 45 gigatons of organic carbon per annum, of which 16 gigatons are exported to the ocean interior. Changes in the magnitude of total and export production can strongly influence atmospheric CO2 levels (and hence climate) on geological time scales, as well as set upper bounds for sustainable fisheries harvest. The two fluxes are critically dependent on geophysical processes that determine mixed-layer depth, nutrient fluxes to and within the ocean, and food-web structure. Because the average turnover time of phytoplankton carbon in the ocean is on the order of a week or less, total and export production are extremely sensitive to external forcing and consequently are seldom in steady state. Elucidating the biogeochemical controls and feedbacks on primary production is essential to understanding how oceanic biota responded to and affected natural climatic variability in the geological past, and will respond to anthropogenically influenced changes in coming decades. One of the most crucial feedbacks results from changes in radiative forcing on the hydrological cycle, which influences the aeolian iron flux and, in turn, affects nitrogen fixation and primary production in the oceans.     

海洋酸化对海水青鳉性别分化的影响

以海水青鳉作为研究对象,研究海洋酸化对其性别分化的影响。将刚受精的受精卵置于对照组(CO_2浓度为480×10~(-6))和2个处理组(CO_2浓度分别为1 000×10~(-6)和2 000×10~(-6))的水体中,直到孵化出膜。将出膜后仔鱼饲养在对照组水体中至性成熟,然后通过形态学、组织学和遗传学方法,对每一尾实验鱼进行表现型和基因型的性别鉴定。经形态学判断,发现酸化处理组的雄雌比例显著高于对照组(P0.01)。经形态学观察其第二性征和遗传学性别判断,对照组的青鳉从孵化到性成熟的个体中并未出现基因型和表现型性别不一致的个体,而在2个酸化处理组中,均有基因型为XX而表现型为雄性的个体,即性逆转雄性,性逆转率分别为38.4%和47.5%。     

Preindustrial to modern interdecadal variability in coral reef pH

The oceans are becoming more acidic due to absorption of anthropogenic carbon dioxide from the atmosphere. The impact of ocean acidification on marine ecosystems is unclear, but it will likely depend on species adaptability and the rate of change of seawater pH relative to its natural variability. To constrain the natural variability in reef-water pH, we measured boron isotopic compositions in a approximately 300-year-old massive Porites coral from the southwestern Pacific. Large variations in pH are found over approximately 50-year cycles that covary with the Interdecadal Pacific Oscillation of ocean-atmosphere anomalies, suggesting that natural pH cycles can modulate the impact of ocean acidification on coral reef ecosystems.     

Elevated Eocene atmospheric CO2 and its subsequent decline

Quantification of the atmospheric concentration of CO2 ([CO2]atm) during warm periods of Earth's history is important because burning of fossil fuels may produce future [CO2]atm approaching 1000 parts per million by volume (ppm). The early Eocene (~56 to 49 million years ago) had the highest prolonged global temperatures of the past 65 million years. High Eocene [CO2]atm is established from sodium carbonate minerals formed in saline lakes and preserved in the Green River Formation, western United States. Coprecipitation of nahcolite (NaHCO3) and halite (NaCl) from surface waters in contact with the atmosphere indicates [CO2]atm > 1125 ppm (four times preindustrial concentrations), which confirms that high [CO2]atm coincided with Eocene warmth.     

Carbon isotope constraints on the deglacial CO₂ rise from ice cores

The stable carbon isotope ratio of atmospheric CO(2) (δ(13)C(atm)) is a key parameter in deciphering past carbon cycle changes. Here we present δ(13)C(atm) data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in δ(13)C(atm) during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the δ(13)C(atm) evolution. During the Last Glacial Maximum, δ(13)C(atm) and atmospheric CO(2) concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then.     

Isotopic evidence for variations in the marine calcium cycle over the Cenozoic

Significant variations in the isotopic composition of marine calcium have occurred over the last 80 million years. These variations reflect deviations in the balance between inputs of calcium to the ocean from weathering and outputs due to carbonate sedimentation, processes that are important in controlling the concentration of carbon dioxide in the atmosphere and, hence, global climate. The calcium isotopic ratio of paleo-seawater is an indicator of past changes in atmospheric carbon dioxide when coupled with determinations of paleo-pH.     

The pace of shifting climate in marine and terrestrial ecosystems

Climate change challenges organisms to adapt or move to track changes in environments in space and time. We used two measures of thermal shifts from analyses of global temperatures over the past 50 years to describe the pace of climate change that species should track: the velocity of climate change (geographic shifts of isotherms over time) and the shift in seasonal timing of temperatures. Both measures are higher in the ocean than on land at some latitudes, despite slower ocean warming. These indices give a complex mosaic of predicted range shifts and phenology changes that deviate from simple poleward migration and earlier springs or later falls. They also emphasize potential conservation concerns, because areas of high marine biodiversity often have greater velocities of climate change and seasonal shifts.     

两种海水酸化模式对马粪海胆(Hemicentrotus pulcherrimus)胚胎早期发育的影响

采用二氧化碳(CO2)和强酸(HCl)模拟海水酸化,研究未来海水酸化对马粪海胆(Hemicentrotus pulcherrimus)胚胎早期发育的影响。根据IPCC预测,实验设置了1个自然海水组、3个CO_2酸化胁迫组:OA1-CO_2(自然海水pH降0.3)、OA_2-CO_2(自然海水pH降0.4)和OA_3-CO_2(自然海水pH降0.5));3个HCl酸化胁迫组:OA_1-HCl(自然海水pH降0.3)、OA_2-HCl(自然海水pH降0.4)和OA_3-HCl(自然海水pH降0.5)。结果显示:1两种海水酸化模式对马粪海胆受精率并无显著影响(P0.05);2与自然海水组相比,两种酸化模式下马粪海胆胚胎上浮率均呈下降趋势,其中OA_1-CO_2组和OA_1-HCl组胚胎上浮率显著降低且差异显著(P0.05),其余各酸化胁迫组胚胎上浮率则呈极显著降低趋势(P0.01);3随着酸化程度的加深,两种酸化模式下马粪海胆四腕浮游幼体存活率较自然海水组均呈下降趋势,与自然海水组相比,OA1-HCl组存活率显著降低(P0.05),其余各酸化胁迫组存活率降低程度极为显著(P0.01);4与自然海水组相比,CO_2酸化胁迫组马粪海胆四腕浮游幼体的对称性缺失现象随酸化程度的加深而加剧,而HCl酸化胁迫对马粪海胆四腕浮游幼体对称性并无明显影响。结果提示,未来海水酸化对马粪海胆早期发育具有重要影响,与HCl酸化模式相比,由CO_2导致的海水酸化对马粪海胆胚胎早期发育的影响更为复杂。     

Simulation of recent global temperature trends

Observations show that global average tropospheric temperatures have been rising during the past century, with the most recent portion of record showing a sharp rise since the mid-1970s. This study shows that the most recent portion of the global temperature record (1970 to 1992) can be closely reproduced by atmospheric models forced only with observed ocean surface temperatures. In agreement with a diverse suite of controversial observational evidence from the past 40 years, the upward trend in simulated tropospheric temperatures is caused by an enhancement of the tropical hydrologic cycle driven by increasing tropical ocean temperatures. Although it is possible that the observed behavior is due to natural climate variability, there is disquieting similarity between these model results, observed climate trends in recent decades, and the early expressions of the climatic response to increased atmospheric carbon dioxide in numerical simulations.     

Comment on "Preindustrial to modern interdecadal variability in coral reef pH"

Based on the boron isotopic composition of coral from the southwestern Pacific, Pelejero et al. (Reports, 30 September 2005, p. 2204) suggested that natural variations in pH can modulate the impact of ocean acidification on coral reef ecosystems. We show that this claim cannot be reconciled with other marine carbon chemistry constraints and highlight problems with the authors' interpretation of the paleontologic data.     

Temporal trends in deep ocean Redfield ratios

The Redfield ratio [carbon:nitrogen:phosphorus (C:N:P)] of particle flux to the deep ocean is a key factor in marine biogeochemical cycling. Changes in oceanic carbon sequestration have been linked to variations in the Redfield ratio on geological time scales, but this ratio generally is assumed to be constant with time in the modern ocean. However, deep-water Redfield ratios in the northern hemisphere show evidence for temporal trends over the past five decades. The North Atlantic Ocean exhibits a rising N:P ratio, which may be related to increased deposition of atmospheric nitrous oxides from anthropogenic N emissions. In the North Pacific Ocean, increasing C:N and C:P ratios are accompanied by rising remineralization rates, which suggests intensified export production. Stronger export of carbon in this region may be due to enhanced bioavailability of aeolian iron. These findings imply that the biological part of the marine carbon cycle currently is not in steady state.     

Role of marine biology in glacial-interglacial CO2 cycles

It has been hypothesized that changes in the marine biological pump caused a major portion of the glacial reduction of atmospheric carbon dioxide by 80 to 100 parts per million through increased iron fertilization of marine plankton, increased ocean nutrient content or utilization, or shifts in dominant plankton types. We analyze sedimentary records of marine productivity at the peak and the middle of the last glacial cycle and show that neither changes in nutrient utilization in the Southern Ocean nor shifts in plankton dominance explain the CO2 drawdown. Iron fertilization and associated mechanisms can be responsible for no more than half the observed drawdown.