Det marine avfallet finnes i strandsonen.

Because det marine avfallet is a definite noun phrase: the marine waste / the marine litter.

In Norwegian, when a noun is definite and has an adjective, you usually get double definiteness:

• det = the definite article for a neuter noun
• marine = the adjective in its definite form
• avfallet = avfallet = the waste, with the definite ending on the noun

So Norwegian often says the equivalent of:

• the + marine + waste-the

That is normal Norwegian structure.

By contrast:

• marine avfall = marine waste / marine litter in a more general or indefinite sense

Because adjectives usually take -e when they are used in a definite phrase.

Compare:

• marint avfall = marine waste / marine litter
  
  • here the noun phrase is not definite
• det marine avfallet = the marine waste
  
  • here the phrase is definite, so the adjective becomes marine

This -e form is very common after den, det, de and in other definite contexts.

No. Here det is not the pronoun it. It is the definite article/determiner that agrees with the noun.

Since avfall is a neuter noun, the phrase uses:

• det for definite singular neuter

So in this sentence:

• det marine avfallet = the marine waste

It is functioning like the, not like it.

Because avfall is a neuter noun, and its definite singular form takes -et.

So:

• et avfall = a waste item / waste
• avfallet = the waste

This is a very common neuter pattern:

• et hus → huset
• et problem → problemet
• et avfall → avfallet

Also, avfall is often used as a mass noun, like waste in English.

In Norwegian, avfall is very often treated as an uncountable mass noun, just like waste in English.

So:

• marint avfall = marine waste / marine litter
• det marine avfallet = the marine waste / the marine litter

Even though in real life it may refer to many objects, the grammar is singular because the noun itself is being treated as a substance/category rather than as individual items.

Yes, in this sentence finnes means something like:

• is found
• can be found
• exists
• is present

So Det marine avfallet finnes i strandsonen means that marine waste is found in or occurs in the shore zone.

This is a very natural Norwegian way to express existence or presence, especially in a slightly formal or factual style.

Because finnes focuses on existence/presence, not just simple location.

Compare:

• finnes = is found / exists / occurs
• er = is
• ligger = lies / is located

So:

• Det marine avfallet finnes i strandsonen
  = marine litter is found in the shore zone

This sounds more like a factual statement in a report, textbook, or environmental description.

If you said:

• Det marine avfallet ligger i strandsonen

that would sound more like the waste is literally lying there physically. That can also work in some contexts, but finnes is more neutral and informational.

Strandsonen is the definite singular form of strandsone, a compound noun:

• strand = shore / beach
• sone = zone

So:

• strandsone = shore zone / shoreline zone / coastal margin
• strandsonen = the shore zone

It is a very typical Norwegian compound noun.

Because Norwegian usually puts definiteness on the noun itself with an ending.

So:

• i strandsonen = in the shore zone

The -en on strandsonen already means the.

You only add a separate determiner like den if you need one for a special structure, especially with an adjective:

• i strandsonen = in the shore zone
• i den brede strandsonen = in the broad shore zone

So without an adjective, i strandsonen is the normal form.

This sentence has normal Norwegian main clause word order:

• Det marine avfallet = subject
• finnes = verb
• i strandsonen = adverbial/place phrase

So it follows the basic pattern:

• Subject + Verb + Place

Norwegian main clauses are V2 clauses, which means the finite verb normally comes in the second position. In this sentence, the subject comes first, so the verb follows it directly.

If you moved the place phrase to the front, the verb would still stay second:

• I strandsonen finnes det marine avfallet.

That is more marked or stylistic, but grammatically fine.

Yes. That would also be correct, but it changes the feel slightly.

• Marint avfall finnes i strandsonen = Marine litter is found in the shore zone
  
  • more general
• Det marine avfallet finnes i strandsonen = The marine litter / the marine waste is found in the shore zone
  
  • more definite or specific

So the version with det ... avfallet sounds more definite, while marint avfall sounds more like a general category.

Here marine means related to the sea or marine environment, not military marines.

So marint/marine avfall means:

• waste in the sea
• waste from the marine environment
• marine litter

In environmental contexts, marin is a very common adjective meaning sea-related.

A careful approximate pronunciation is:

• Det marine avfallet finnes i strandsonen
• roughly: deh mah-REE-neh AHV-fal-eh fin-ess ee STRAHND-soh-nen

A few useful notes:

• det is often pronounced more like deh in connected speech
• marine has stress on the second syllable: ma-RI-ne
• avfallet has the definite ending -et, often pronounced lightly
• strandsonen is a compound, but said smoothly as one word

The exact pronunciation will vary by dialect, but that approximation is good enough for a learner to start with.