Anthropogenic climate change has altered primary productivity in Lake Superior.

Anthropogenic climate change has the potential to alter many facets of Earth's freshwater resources, especially lacustrine ecosystems. The effects of anthropogenic changes in Lake Superior, which is Earth's largest freshwater lake by area, are not well documented (spatially or temporally) and predicted future states in response to climate change vary. Here we show that Lake Superior experienced a slow, steady increase in production throughout the Holocene using (paleo)productivity proxies in lacustrine sediments to reconstruct past changes in primary production. Furthermore, data from the last century indicate a rapid increase in primary production, which we attribute to increasing surface water temperatures and longer seasonal stratification related to longer ice-free periods in Lake Superior due to anthropogenic climate warming. These observations demonstrate that anthropogenic effects have become a prominent influence on one of Earth's largest, most pristine lacustrine ecosystems.

The methane cycle in ferruginous Lake Matano.

In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigenic organic matter is degraded through methanogenesis, despite high abundances of Fe (hydr)oxides in the lake sediments. Biogenic CH4 accumulates to high concentrations (up to 1.4 mmol L⁻¹) in the anoxic bottom waters, which contain a total of 7.4 × 105 tons of CH4. Profiles of dissolved inorganic carbon (ΣCO2) and carbon isotopes (δ¹³C) show that CH4 is oxidized in the vicinity of the persistent pycnocline and that some of this CH4 is likely oxidized anaerobically. The dearth of NO3⁻ and SO4²â» in Lake Matano waters suggests that anaerobic methane oxidation may be coupled to the reduction of Fe (and/or Mn) (hydr)oxides. Thermodynamic considerations reveal that CH4 oxidation coupled to Fe(III) or Mn(III/IV) reduction would yield sufficient free energy to support microbial growth at the substrate levels present in Lake Matano. Flux calculations imply that Fe and Mn must be recycled several times directly within the water column to balance the upward flux of CH4. 16S gene cloning identified methanogens in the anoxic water column, and these methanogens belong to groups capable of both acetoclastic and hydrogenotrophic methanogenesis. We find that methane is important in C cycling, even in this very Fe-rich environment. Such Fe-rich environments are rare on Earth today, but they are analogous to conditions in the ferruginous oceans thought to prevail during much of the Archean Eon. By analogy, methanogens and methanotrophs could have formed an important part of the Archean Ocean ecosystem.

BMP signaling is required for heart formation in vertebrates.

In these studies, we have taken advantage of a transient transgenic strategy in Xenopus embryos to demonstrate that BMP signaling is required in vivo for heart formation in vertebrates. Ectopic expression of dominant negative Type I (tALK3) or Type II (tBMPRII) BMP receptors in developing Xenopus embryos results in reduction or absence of heart formation. Additionally, blocking BMP signaling in this manner downregulates expression of XNkx2-5, a homeobox gene required for cardiac specification, prior to differentiation. Notably, however, initial expression of XNkx2-5 is not affected. Mutant phenotypes can be rescued by co-injection of mutant with wild-type receptors or co-injection of mutant receptors with XSmad1, a downstream mediator of BMP signaling. Whole-mount in situ analyses indicate that ALK3 and XSmad1 are coexpressed in cardiogenic regions. Together, our results demonstrate that BMP signaling is required for maintenance of XNkx2-5 expression and heart formation and suggest that ALK3, BMPRII, and XSmad1 may mediate this signaling.

Impact of environmental noise on oscillatory pattern formation in crystal growth: plagioclase feldspar

Recently, a model for oscillatory zoning in a geochemical system (plagioclase feldspar) was proposed. In that model, oscillations in the composition are generated through a Hopf bifurcation. In this paper, the effects of fluctuations of the bulk composition are studied by means of computer simulations. It is shown that environmental noise can lead to pattern formation such as oscillatory zoning, even when no deterministic periodic solutions exist. The fluctuations in the bulk composition thus lead to an enlargement of the range of system's variables values for which oscillatory zoning occurs. Coherence resonance close to the Hopf bifurcation is also observed in such a system.