Determination of ammonia

Sea ice has not always existed in the Arctic and indeed little is known about the sea-ice history of this climatically sensitive region. The recent discovery of ice-rafted debris in middle Eocene ocean sediments prompted suggestions that ice appeared in the Arctic about 46 million years ago, but it is important to distinguish between land-based glacial ice and sea ice as the source of the debris because each kind of ice has different climate implications. Now the analysis of an oceanic sediment core from the ACEX project reveals vast quantities of well-preserved fossils of the needle-like diatom Synedropsis spp., which relied on sea ice for its survival, at about 260 metres below the sea floor of the central Arctic. This, in combination with detailed grain analysis, suggests that sea ice was the dominant source of ice-rafted debris at around 47.5–45.5 million years ago. The results push back the first appearance of ice in the Arctic by 1.25 million years, and the first appearance of sea-ice diatoms by 16 million years. The presence of ice-rafted debris (IRD) in middle Eocene ocean sediments has previously been demonstrated, but it has been unclear whether the source of IRD was land-based glacial ice or sea ice, a distinction with important climate implications. The analysis of a sediment core from the ACEX project now reveals evidence that sea ice was the dominant source for IRD from 47.5 to 45.5 million years ago. Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic1, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago2,3. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice4, IRD records2,3 are restricted to providing a history of general ice-rafting only. It is critical to differentiate sea ice from glacial (land-based) ice as climate feedback mechanisms vary and global impacts differ between these systems: sea ice directly affects ocean–atmosphere exchanges5, whereas land-based ice affects sea level and consequently ocean acidity6. An earlier report3 assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists2, these data are neither comprehensive nor quantified. Here we show the presence of middle Eocene Arctic sea ice from an extraordinary abundance of a group of sea-ice-dependent fossil diatoms (Synedropsis spp.). Analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of IRD at this time. Together with new information on cosmopolitan diatoms and existing IRD records2, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas ∼47.5 Myr ago, followed ∼0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic. Our data establish a 2-Myr record of sea ice, documenting the transition from a warm, ice-free3 environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase7.

Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris.

Neotropical coastal lagoons (NCL) are human-dominated ecosystems. Their distribution along densely populated coastal areas of developing countries makes these systems among the most threatened in the world. Here, we summarize some aspects of the causes and consequences of NCL biodiversity, their functioning, their importance to the surrounding populations, their fragility, and their responses to local and global anthropogenic impacts and the challenges that Neotropical countries face in conserving these systems. Although still scarce and geographically concentrated, a growing body of studies has shown that NCLs are physiographically diversified systems, which harbor a considerable and particular proportion of the Neotropical inland aquatic biodiversity. Despite the fact that coastal lagoons are ecotones that are intricately connected to surrounding environments, they develop mechanisms for structural and functional regulation, which confer to these systems higher productivity and carrying capacities than surrounding ecosystems. Such traits attract residential developments and subsidize local traditional populations with important economic and aesthetic ecosystem revenues such as fisheries and scenic beauty. However, the disorganized human occupation around NCLs are causing profound impacts such as eutrophication, salinization, exotic species introduction, as well as other effects, which are ultimately imposing major habitat degradations and biodiversity extirpations in NCLs. We argue that interdisciplinary conservation strategies, which integrate scientific expertise, government officials, private companies and the general public, are the most likely to overcome the geographic and economic obstacles to NCL conservation.

/pdf/neotropical-coastal-lagoons-an-appraisal-of-their-fgtgaki22z.pdf

Neotropical coastal lagoons: an appraisal of their biodiversity, functioning, threats and conservation management.

Sieves and flaps: siliceous minutiae in pores of raphid diatoms.

Reynolds Functional Groups (RFG) were designed to represent the diversity of phytoplankton assemblages of freshwater ecosystems and are among the most enduring legacies of C. S. Reynolds to freshwater phytoplankton ecologists. The RFG concept summarises a rich base of knowledge, clustering species according to functional criteria. RFG allow researchers to organise information, understand community and ecosystem functioning, and identify future outcomes, also contributing to construct hypotheses and define community assembly. This approach represents the environmental requirements, tolerances and sensitivities of species, organizing them into diagnostic environmental axes representing the habitat template of phytoplankton communities. In this contribution, we highlight the importance of this trait-based approach for phytoplankton ecology, and summarise its history and usage for phytoplankton species classifications and prediction based on environmental gradients. We present some of the applications of the approach, to describe patterns, explain mechanisms and predict new situations. We hope that this review will contribute both to describe the trajectory and practice of RFG and to encourage its use in addressing new ecological questions and in generating new avenues of research.

Reynolds Functional Groups: a trait-based pathway from patterns to predictions

A new Synedropsis species is described from a coastal tropical lagoon in south-eastern Brazil. This species has a single chloroplast in both views of the valve, apical pore fields composed of three slits, and uniseriate striae. It is planktonic and was found in brackish water. Synedropsis roundii is the eighth Synedropsis species to be described and the first to be found in a tropical region. We studied the seasonal dynamics of S. roundii, which can form blooms in the coastal Imboassica Lagoon, Rio de Janeiro stale, Brazil. Continuous mixing of this shallow environment is suggested to be an important physical factor determining the success of the species. Availability of soluble reactive silicon is thought to be the main factor regulating the large biomass fluctuations. In the classification of Reynolds in 1997 (Vegetation processes in the pelagic: a model for ecosystem theory. Ecology Institute, Oldendorf, Germany, 371 pp.), S. roundii appears to belong to D-assemblage, a set of small and fast-g...

Taxonomy and ecology of Synedropsis roundii sp. nov. (Bacillariophyta) from a tropical brackish coastal lagoon, south-eastern Brazil

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Taxonomy and ecology of Synedropsis roundii sp. nov. (Bacillariophyta) from a tropical brackish coastal lagoon, south-eastern Brazil