Description: ENGLISH ABSTRACT: The article summarizes the hydrographic-hydrochemical conditions in the western and central Baltic Sea in 2017. Based on meteorological conditions, the horizontal and vertical distribution of temperature, salinity, oxygen/hydrogen sulphide and nutrients are described on a seasonal scale. For the southern Baltic Sea area, the “cold sum” of the air temperature of 31.7 Kd in Warnemünde amounted to a mild winter in 2014/15 and ranks as 15th warmest winter since the beginning of the record in 1948. The summer “heat sum” of 159.5 Kd ranks on 28th position of the warmest summers over the past 70 years and is slightly above the long-term average of 153.4 Kd. Based on satellite derived Sea Surface Temperature (SST) 2017 was the eleventh-warmest year since 1990 and with 0.24 K slightly above the long-term SST average. March, April and October - December contributed to the average by their positive anomalies. July and August were characterized by negative anomalies. The anomalies reached maximum values of +2 K and -3 K. The situation in the deep basins of the Baltic Sea was mainly coined by beginning stagnation at bottom-near water depths of the eastern Gotland Basin and ongoing ventilation of the upper part 5 of the deep-water above 150 m as a consequence of weak inflows. For the first time within this phase of intensified inflow activity, starting in 2014, the ventilation of the Farö Deep at the Northern Central Basin was registered at the beginning of the year. In the course of 2017 two weak inflows showing total volumes of 210 km^³ (February) and 188 km^³ (October) were registered. In conclusion, the impact of the observed phase of intensified water exchange processes with subsequent consequences for the biogeochemical cycles is weakening.GERMAN ABSTRACT: Die Arbeit beschreibt die hydrographisch-hydrochemischen Bedingungen in der westlichen und zentralen Ostsee für das Jahr 2017. Basierend auf den meteorologischen Verhältnissen werden die horizontalen und vertikalen Verteilungsmuster von Temperatur, Salzgehalt, Sauerstoff/ Schwefelwasserstoff und Nährstoffen mit saisonaler Auflösung dargestellt. Für den südlichen Ostseeraum ergab sich eine Kältesumme der Lufttemperatur an der Station Warnemünde von 31,7 Kd. Im Vergleich belegt der Winter 2016/17 den 15. Platz der wärmsten Winter seit Beginn der Aufzeichnungen im Jahr 1948 und wird als mild klassifiziert. Mit einer Wärmesumme von 159,5 Kd rangiert der Sommer im Mittelfeld der 70jährigen Datenreihe und reiht sich auf Platz 28 der wärmsten Sommer ein. Das Langzeitmittel liegt bei 153,4 Kd. Auf der Grundlage von satellitengestützten Meeresoberflächentemperaturen (SST) war 2017 das elft- wärmste Jahr seit 1990 und mit 0,24 K etwas über dem langfristigen SST-Mittel. März, April und Oktober - Dezember trugen durch ihre positiven Anomalien zum Durchschnitt bei. Juli und August waren durch negative Anomalien gekennzeichnet. Die Anomalien erreichten Höchstwerte von +2 K und -3 K. Die Situation in den Tiefenbecken der Ostsee war im Wesentlichen geprägt durch bodennah einsetzende Stagnation im östlichen Gotland Becken und Belüftung der mittleren Wassersäule oberhalb 150 m im Zuge kleinerer Einströme. Zu Jahresbeginn wurde das im nördlichen Zentralbecken gelegene Farö Tief erstmals innerhalb der aktuellen Einstromphase belüftet. Im Jahresverlauf 2017 wurden zwei weitere schwache Einströme mit Volumina zwischen 210 km³ und 188 km³ im Februar sowie Oktober registriert. Zusammenfassend kann gesagt werden, dass die Auswirkungen der seit 2014 beobachten Phase von verstärkten Wasseraustauschprozessen mit entsprechenden Konsequenzen für die biogeochemischen Kreisläufe abklingen.

Description: Understanding the development of primary production is essential for projections of the global carbon cycle in the context of climate change. A chlorophyll a hindcast that serves as a primary production indicator was obtained by fitting in situ measurements of nitrate, chlorophyll a, and temperature. The resulting fitting functions were adapted to a modeled temperature field. The method was applied to observations from the Madeira Basin, in the northeastern part of the oligotrophic North Atlantic Subtropical Gyre and yielded a chlorophyll a field from 1989 to 2008 with a monthly resolution validated with remotely measured surface chlorophyll a data by SeaWiFS. The chlorophyll a hindcast determined with our method resolved the seasonal and interannual variability in the phytoplankton biomass of the euphotic zone as well as the deep chlorophyll maximum. Moreover, it will allow estimation of carbon uptake over long time scales.

Description: The subtropical northeast Atlantic has previously been identified as a marine environment with an apparent imbalance between low nitrate supply to the surface and concurrent high export production. To better constrain the sources and fluxes of mixed layer nitrate and to assess the potential role of N2 fixation in providing new nitrogen (N), we investigated the depth distribution of nitrate δ15N and δ18O at six stations across the Azores Front in the NE Atlantic. In addition, we measured the δ15N of dissolved organic N (DON) in surface waters and of sinking particulate N collected in sediment traps at 2000 m depth between 2003 and 2005 at Station KIEL276. The nitrate isotope profiles at the majority of the hydrographic stations displayed a decrease in the δ15N from depth toward low-nitrate surface waters, concomitant with an increase in δ18O. Given that nitrate uptake by phytoplankton leads to a proportional increase in nitrate δ15N and δ18O, the observed surface water nitrate isotope anomalies (Δ(15;18) up to −6‰) indicate that nitrate assimilation is not the sole process controlling the isotopic composition of nitrate in the photic zone and implicate a significant addition of newly fixed N that is remineralized in surface and subsurface waters. Both the concentration of DON and its δ15N in surface water were spatially invariant, showing mean values of 4.7 ± 0.5 μmol L−1 and 2.6 ± 0.4‰ (n = 35), respectively, supporting the conjecture of a mostly recalcitrant DON pool. The weighted biannual mean δ15N of sinking particulate N (1.8 ± 0.8‰, n = 33) was low with respect to thermocline nitrate. The anomalous dual nitrate isotope signatures together with the low δ15N of export production and elevated nitrate-to-phosphate ratios in surface and subsurface waters strongly suggest that N2 fixation represents a substantive source of N in this part of the subtropical northeast Atlantic. Simple isotope mass balance suggests that, locally, N2 fixation supplies between 56 and 259 mmol N m−2 a−1 for phytoplankton growth in the photic zone, accounting for up to ∼40% of the estimated export production.

Description: Lisbon (Portugal)- Vigo (Spain), 04.05.2013 to 19.05.2013

Description: A chlorophyll a hindcast in the Madeira Basin from 1871 to 2008 was used to analyze the long-term variability in the oligotrophic, subtropical gyres in relation to the climate change of the last century. The deep chlorophyll maximum (DCM), as dominant pattern of the chlorophyll a field, showed a fast decrease in its strength in the 1940s. An absolute minimum was reached between 1967 and 1973 when no DCM established with a recovering to the end of the time series. Long-term variability of the DCM was related to the North Atlantic Oscillation with a time delay of 9 years. The marked decrease in the 1940s was correlated to the drop of the solar radiation in transition from early brightening to global dimming. Caused by the influence of the solar radiation and maybe related to increasing global temperatures in the last century, the integrated chlorophyll a concentration decreased by about 0.7 mg m−2 in 2008 compared to 1871. The high-resolved chlorophyll a hindcast allowed an estimation of the carbon uptake by the ocean due to primary production in the euphotic zone. A rough calculation over the area of the global subtropical oceans showed 700 megaton less carbon uptake in 2008.