Publication Abstract

The Integrated North Sea Programme (INP)

The Integrated North Sea Programme (INP)

H. Van Haren, P. Ruardij, H. Ridderinkhof and D.K. Mills

We present detailed (hourly sampled) bio-optical and physical data from an extensive (27 months in four years) mooring programme in the central North Sea (Oyster Grounds). The purpose of the programme was a detailed study on the variability of phytoplankton abundance and the, possibly associated, impact of vertical exchange by atmospheric disturbances across the (seasonal) thermocline. After this campaign, we conclude that sophisticated moorings are not yet adequate for long-tern, routine oceanographic monitoring purposes, as the instruments generally need too much attendance by regular in-situ calibration and servicing (at least once a month). The data analysis showed that no observational evidence has been found for the spring bloom to enhance the (onset of) stratification or vice versa for the stratification to favour the spring bloom.

Instead, a spring bloom is found before the stratification becomes well established and, prior to that, a subtle dependance of the evolution of the spring bloom has been found on the turbulence intensity in the water column. From a numerical model, in which we used the observations for initiaition and verification, it became clear that the timing of the onset of stratification is critical for the entire growth season. In summer no sub-surface maximum in chlorophyll was observed at our mooring site, because sufficient irradiation reached to the bottom. Despite the strong stratification, a bloom developed after a strong (convective) mixing event in late summer, and another one also prior to that, probably after internal mixing events induced by strong current shear across the pycnocline, although the role of horizontal advection could not be ruled out entirely.

Reference:

H. Van Haren, P. Ruardij, H. Ridderinkhof and D.K. Mills, 1997. The Integrated North Sea Programme (INP). pp529-538,. In: Operational Oceanography. The Challenge for European Co-operation. Edited by J.H. Stel, et al., Elsevier Science B.V.

H. Van Haren, P. Ruardij, H. Ridderinkhof and D.K. Mills*

pp529-538,. In: Operational Oceanography. The Challenge for European Co-operation. Edited by J.H. Stel, et al., Elsevier Science B.V.