Alaska red algae are the first to show the influence of climate phenomena on subarctic regions

Alaska red algae: The red alga Clathromorphum grows in the shallow waters of the subarctic North Pacific and the Bering Sea. Unlike many other algae, Clathromorphum forms a hard calcareous skeleton similar to, for example, tropical coral. Numerous sea urchins and seaweed colonize the algae and form a sensitive ecosystem. © University of Göttingen

Read out

Red algae can record the climate of the past in their limestone skeleton. Now researchers have discovered a more than 100-year-old specimen of the genus Clathromorphum nereostratum off the Aleutian Islands, which turned out to be a precise climate archive: The red alga provided for the first time a precise annually resolved climate reconstruction of the sub-Arctic North Pacific. The new data show that the El Niño phenomenon also has an effect in these regions and thus unfolds a hitherto unknown long-range effect.

In the course of the current climate discussion, scientists are intensively searching for geological archives that can provide climate-relevant parameters of bygone eras. These include, for example, calcifying organisms, ice sheets and the tree rings of trees. These periodically changeable systems are characterized by chemical variation, different isotopic composition or a change in the length of growth.

117 years of climate history recorded

However, the data obtained often provide only limited information about the climate of the past, because there are no benchmarks for verifying the results and therefore the various geo-systems can only be "calibrated" insufficiently. However, scientists have now discovered a "powerful" climate archive for the cold regions of the Pacific Ocean with particularly long-lived coral red algae that form solid limestone skeletons and stick to one place. The chemical composition and the isotopic signature of their limestone skeletons can provide information about climate changes of the past.

A copy of the red alga clathromorphum, which is being studied near the coast of the Aleutian island of Attu in the Pacific Ocean by geochemists from the University of Göttingen together with colleagues from Germany, the USA and Canada, has recorded the past 117 years of climate history. The chemical composition of the algae skeleton captured researchers around Andreas Kronz at the Geoscientific Center of the University of Göttingen recorded using an electron microprobe.

The magnesium levels in the calcium carbonate reflect the annual temperature fluctuations, according to the researchers in the journal Geophysical Research Letters. In addition, the oxygen isotope signature is directly coupled to the water temperature in the main growth phase of the algae. display

Calibration of the "thermometer" is necessary

Growth bands: The calcified red algae show growth bands, which are formed similar to tree rings in annual cycles. Growth bands are clearly visible in the detail view. Chemical analysis of the belts, which have average thicknesses of only about 0.35 mm per year, draw conclusions about the water temperatures in which the red algae lived. The red alga archives therefore climate events and temperatures of the past centuries. University of Gttingen

To determine the isotopic composition, samples of 0.05 milligram of substance are sufficient. They are taken from the growth bands of red algae using a specially designed micro-pulp. The calibration of the "thermometer" will be carried out on the most recent growth stages of various red seaweed species from the Gulf of California and waters off Newfoundland, for which accurate temperature data are available.

The Aleutian Red Valley data provide insights into the causes of dramatic changes in the North Pacific ecosystems that have been observed for a long time: they indicate warming and increasing erosion of the surface Wasschenwassers since the mid-20th century. The found time series agrees with the so-called "Pacific Decadal Oscillation". This is a change in sea surface temperature that occurs approximately every 25 years. To the surprise of the researchers, the oxygen data also show a further four-year climate change.

It can be associated with the El Ni o phenomenon, the appearance of unusual, altered currents in the oceanographic-meteorological system of the South Pacific. Kronz: "Although it is known that El Ni o activity also influences the climate of the northern hemisphere. However, a direct marine influence in the Aleutian area was previously unknown. "

(idw - University of Gttingen, 02.08.2007 - DLO)