Subterranean estuaries (STE) underneath high-energy beaches are dynamic interfaces for the exchange of dissolved organic matter (DOM) and nutrients between marine and terrestrial environments. Beach wrack deposited during tides and waves and leached during tidal inundation, wave swash and precipitation contributes DOM and nutrients to STEs. Wrack is often considered a nuisance in recreational beach use, but its removal could deprive the organic-poor ecosystem of an important energy source. The complex interplay of environmental factors influencing the release of DOM and nutrients from beach wrack remains poorly understood, making it difficult to assess its role in sustaining the beach bioreactor. To address this knowledge gap, we conducted a comprehensive beach wrack leaching experiment. We collected wrack typically found along the North Sea shoreline like bladder wrack (Fucus sp.), jellyfish (Aurelia sp.) and terrestrial plant and peat debris. Inundation by tides or precipitation was simulated by submerging wrack subsamples in artificial sea- and rainwater with conductivities typical for the North Sea coast. In addition, we simulated solar weathering by irradiating wrack subsamples with UVA light and subsequently leached the wrack subsamples with artificial seawater. Leaching media were then analyzed for dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations. DOM was desalted and analyzed using ultra-high-resolution mass spectrometry, yielding thousands of molecular formulae for each wrack sample and treatment type. Our results showed substantial releases of DOC and TDN from Fucus sp., and high TDN concentrations from Aurelia sp. wrack in artificial seawater incubations. In wrack-derived DOM, we unveiled a predominance of molecular formulae characteristic of biochemical building blocks like sugars, amino acids, and vitamins. This suggests that the DOM leached from beach wrack could provide a valuable source of energy and nutrients for microbial communities in these systems. Notably, our findings also included high abundances of aromatic and humic-like DOM in macroalgal beach wrack, which could complicate the interpretation of marine and terrestrial source-sink molecular proxies. DOM and nutrients released from beach wrack were type- and treatment specific. We recommend the inclusion of wrack-derived inputs into reactive transport models and posit that wrack and consumer species composition at beach STEs could be tightly linked.