The dataset presents data from a laboratory experiment exploring the effect of heatwaves of different intensities on benhic bioturbation, community excretion and biogeochemical cycling of solutes. We tested the effects of short-term, moderate and strong marine heatwaves on macrofauna bioturbation and associated solute fluxes as examples of ecosystem functioning. We also measured macrofaunal excretion rates to assess effects of temperature on macrofauna metabolism. For this experiment, we used unmanipulated sediment cores with natural animal communities collected from a muddy location at 32 m depth in the northern Baltic Sea. Despite the mechanistic effect of bioturbation remaining unchanged between the treatments, there were significant differences in oxygen consumption, solute fluxes and excretion. Biogeochemical and biological processes were boosted by the moderate heatwave, whereas biogeochemical cycling seemed to decrease under a strong heatwave.

Sediment cores used as experimental units were retrieved with a GEMAX twin-corer (diameter 9 cm) from a 32 m deep, muddy site (coordinates 59° 51 614 N 23° 20 943 E) in the northern Baltic Sea. All temperature treatments (in situ, Moderate and Strong) had five replicate cores. The following parameters were measured: sediment mixing (DbN) using luminophore tracers, maximum penetration depth (MPD) using luminophore tracers, porewater exchange rate (Q) using an inert bromide tracer, fluxes of nitrate+nitrite, phosphate, silicate and ammonium and oxygen (Winkler titration), benthic ocmmunity excretion rates of ammonium and phosphate and community composition of macrofauna. The solute fluxes were measured as start and end concentrations at the start and end of dark incubations and calculated to a flux per square meter per day. Excretion rates are given per core per day. Sediment mixing is given as square cm per year, porewater exchange rate as ml per day and MPD as cm into the sediment. Sediment characteristics are measured at the end of the 9-day long experiment from one core per treatment which was sliced in 0.5 cm intervals down to 5 cm, in 1 cm intervals down to 9 cm and in 2 cm intervals down to as long as there was sediment in the core. Seidment organic content is given as % Loss on Ignition, chl a and phaeophytin as ug per gram of sediment and carbon and nitrogen as C/N ratio.