Radiance, irradiance, and remote sensing reflectance during the North Sea Coast Harmful Algal Bloom (NORCOHAB II) HEINCKE cruise HE302

In this study four data quality flags are presented for automated and unmanned above-water hyperspectral optical measurements collected underway in the North Sea, The Minch, Irish Sea and Celtic Sea in April/May 2009. Coincident to these optical measurements a DualDome D12 (Mobotix, Germany) camera system was used to capture sea surface and sky images. The first three flags are based on meteorological conditions, to select erroneous incoming solar irradiance (ES) taken during dusk, dawn, before significant incoming solar radiation could be detected or under rainfall. Furthermore, the relative azimuthal angle of the optical sensors to the sun is used to identify possible sunglint free sea surface zones. A total of 629 spectra remained after applying the meteorological masks (first three flags). Based on this dataset, a fourth flag for sunglint was generated by analysing and evaluating water leaving radiance (LW) and remote sensing reflectance (RRS) spectral behaviour in the presence and absence of sunglint salient in the simultaneously available sea surface images. Spectra conditions satisfying "mean LW (700-950 nm) < 2 mW/m**2/nm/Sr" or alternatively "minimum RRS (700-950 nm) < 0.010/Sr", mask the most measurements affected by sunglint, providing efficient flagging of sunglint in automated quality control. It is confirmed that valid optical measurements can be performed 0° <= theta <= 360° although 90° <= theta <= 135° is recommended.

Dissolved iron and Fe(II) in an iron induced Southern Ocean phytoplankton bloom measured during TANGAROA cruise SOIREE

During the 13 day Southern Ocean Iron RE-lease Experiment (SOIREE), dissolved iron concentrations decreased rapidly following each of three iron-enrichments, but remained high (>1 nM, up to 80% as FeII) after the fourth and final enrichment on day 8. The former trend was mainly due to dilution (spreading of iron-fertilized waters) and particle scavenging. The latter may only be explained by a joint production-maintenance mechanism; photoreduction is the only candidate process able to produce sufficiently high FeII, but as such levels persisted overnight (8 hr dark period) -ten times the half-life for this species- a maintenance mechanism (complexation of FeII) is required, and is supported by evidence of increased ligand concentrations on day 12. The source of these ligands and their affinity for FeII is not known. This retention of iron probably permitted the longevity of this bloom raising fundamental questions about iron cycling in HNLC (High Nitrate Low Chlorophyll) Polar waters.

Biogenic silica in the coastal plume of the Mississippi River

The surface distributions of dissolved silicic acid, chlorophyll and diatom abundance were measured in the plume of the Mississippi River and adjacent waters during spring (late April and early May 1993) and summer (July 1992). In spring, the time of maximum river flow, there was an intense diatom bloom with a mean diatom abundance of 1.5 x 10**7 cells/l, more than an order of magnitude higher than in summer. Mixing curves of silicic acid concentration ([Si(OH)4]) versus salinity indicate that biological uptake within the river plume removed >99% of the Si(OH)4 supplied by the river in spring and 80 to 95% in summer. In spring [Si(OH)4] was occasionally depleted to <0.2 µM-among the lowest values ever reported from the ocean-with extensive depletion to >=0.5 µM over the shelf. In summer [Si(OH)4] was less severely depleted; the lowest measured was 0.93 µM and all others were >=2.4 µM. 30Si kinetic experiments were performed during both spring and summer to measure the degree to which the rate of Si uptake by the natural diatom assemblages was limited in situ by substrate availability. In spring the dependence of the specific uptake rate (V) on extracellular [Si(OH)4] conformed much more closely to the Michaelis-Menten saturation function than has been observed in past studies. Strong dependence of V on [Si(OH)4] was observed throughout the most Si(OH)4-depleted (<0.5 µM) region, where V was limited to 12 to 45% of the diatom assemblages' maximum uptake rate (Vmax). Half-saturation concentrations for Si uptake (Ks) averaged 0.85 uM (range = 0.48 to 1.71; n = 7) in spring, with the lowest values equal to the lowest previously reported for natural diatom assemblages. There was only 1 station in summer where V was limited by [Si(OH)4], and at that station Ks was 5.3 µM-quite high in comparison with previous studies. At stations where V was limited by [Si(OH)4], in both spring and summer, Chaetoceros spp. were numerically dominant; where there was no Si limitation other diatoms, usually Skeletonema costatum, dominated. The data thus indicate strong Si limitation in spring, with diatom assemblages well adapted to low [Si(OH)4], but little or no Si limitation in summer. Historical data suggest that coastal Si(OH)4 depletion and Si limitation may be recent phenomena in the northern Gulf of Mexico, resulting from increasing [NO3-] and decreasing [Si(OH)4] in the Mississippi River during the past 30 to 50 yr.

Biogenic and lithogenic silica, silicic acid, production of biogenic silica, and irradiance measurements during the Ross Sea Bloom Project 1994-1996

The development of the seasonal phytoplankton bloom in the Ross Sea was studied during two cruises. The first, conducted in November-December 1994, investigated the initiation and rapid growth of the bloom, whereas the second (December 1995-January 1996) concentrated on the bloom's maximum biomass period and the subsequent decline in biomass. Central to the understanding of the controls of growth and the summer decline of the bloom is a quantitative assessment of the growth rate of phytoplankton. Growth rates were estimated over two time scales with different methods. The first estimated daily growth rates from isotropic incorporation under simulated in situ conditions, including 14C, 15N and 32Si uptake measurements combined with estimates of standing stocks of particulate organic carbon, nitrogen and biogenic silica. The second method used daily to weekly changes in biomass at selected locations, with net growth rates being estimated from changes in standing stocks of phytoplankton. In addition, growth rates were estimated in large-volume experiments under optimal irradiances. Growth rates showed distinct temporal patterns. Early in the growing season, short-term estimates suggested that growth rates of in situ assemblages were less than maximum (relative to the temperature-limited maximum) and were likely reduced due to low irradiance regimes encountered under the ice. Growth rates increased thereafter and appeared to reach their maximum as biomass approached the seasonal peak, but decreased markedly in late December. Differences between the major taxonomic groups present were also noted, especially from the isotopic tracer experiments. The haplophyte Phaeocystic antarctica was dominant in 1994 throughout the growing season, and it exhibited the greatest growth rates (mean 0.41/day) during spring. Diatom standing stocks were low early in the growing season, and growth rates averaged 0.100/day. In summer diatoms were more abundant, but their growth rates remained much lower (mean of 0.08/day) than the potential maximum. Understanding growth rate controls is essential to the development of predictive models of the carbon cycle and food webs in Antarctic waters.

Contribution of woody habitat islands to the conservation of birds and their potential ecosystem services in an extensive Colombian rangeland

The conservation of birds and their habitats is essential to maintain well-functioning ecosystems including human-dominated habitats. In simplified or homogenized landscapes, patches of natural and semi-natural habitat are essential for the survival of plant and animal populations. We compared species composition and diversity of trees and birds between gallery forests, tree islands and hedges in a Colombian savanna landscape to assess how fragmented woody plant communities affect forest bird communities and how differences in habitat characteristics influenced bird species traits and their potential ecosystem function. Bird and tree diversity was higher in forests than in tree islands and hedges. Soil depth influenced woody species distribution, and canopy cover and tree height determined bird species distribution, resulting in plant and bird communities that mainly differed between forest and non-forest habitat. Bird and tree species and traits widely co-varied. Bird species in tree islands and hedges were on average smaller, less specialized to habitat and more tolerant to disturbance than in forest, but dietary differences did not emerge. Despite being less complex and diverse than forests, hedges and tree islands significantly contribute to the conservation of forest biodiversity in the savanna matrix. Forest fragments remain essential for the conservation of forest specialists, but hedges and tree islands facilitate spillover of more tolerant forest birds and their ecological functions such as seed dispersal from forest to the savanna matrix.