Changing nutrient cycling in Lake Baikal, the world’s oldest lake

Lake Baikal, lying in a rift zone in southeastern Siberia, is the world's oldest, deepest, and most voluminous lake that began to form over 30 million years ago. Cited as the “most outstanding example of a freshwater ecosystem” and designated a World Heritage Site in 1996 due to its high level of endemicity, the lake and its ecosystem have become increasingly threatened by both climate change and anthropogenic disturbance. Here, we present a record of nutrient cycling in the lake, derived from the silicon isotope composition of diatoms, which dominate aquatic primary productivity. Using historical records from the region, we assess the extent to which natural and anthropogenic factors have altered biogeochemical cycling in the lake over the last 2,000 y. We show that rates of nutrient supply from deep waters to the photic zone have dramatically increased since the mid-19th century in response to changing wind dynamics, reduced ice cover, and their associated impact on limnological processes in the lake. With stressors linked to untreated sewage and catchment development also now impacting the near-shore region of Lake Baikal, the resilience of the lake’s highly endemic ecosystem to ongoing and future disturbance is increasingly uncertain

Linewidth of collimated wavelength-converted emission in Rb vapour

We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power continuous-wave laser radiation at 780 and 776 nm and an internally generated mid-IR field at 5.23 μm in Rb vapour. Using a high-finesse Fabry–Perot interferometer, the spectral width of the CBL is found to be <1.3 MHz for a wide range of experimental conditions. We demonstrate using frequency-modulated laser light that the CBL linewidth is mainly limited by the temporal coherence of the applied laser fields rather than the atom–light interaction itself. The obtained result allows the same 1.3 MHz upper limit to be set for the linewidth of the collimated mid-IR radiation at 5.23 μm, which has not been directly detected.Alexander Akulshin, Christopher Perrella, Gar-Wing Truong, Andre Luiten, Dmitry Budker, Russell McLea